hi, just read this and thought i'd pop in with a bit of advice if that's ok... well, a kind of step by step instruction...
These type of screens and rubbers are known as a 'string-in', because you'll need a length of rope to fit them, you can do it without but it is a right pain....anyway, here we go...
please do everything slowly and carefully at all times, don't rush it, it will crack
Before you start shove the new rubber in a bucket of hot water, not scalding hot, just hot. It makes it so much easier to handle.
Remove all shiny trim from the rubber and spray with a detergent/water mix, it will run into the rebate when the seal is coming out and aid removal. working inside the car gently apply pressure to the top corners and all along the top edge, working slowly, some more detergent or a windscreen cleaning solution will help here also. You are aiming to get the top inner edge of the seal past the lip of the shell, you can use a blunt plastic or wooden tool to aid pushing the seal out, there is proper 'ball ended' tool for this job, but these can slip and you can crack the screen quite easily with it, a inch wide flat blunted 'spade ended' homemade tool is much better. Be careful as once it's started to go it will start to pull itself out and can tear the rubber, if you're fitting a new one this won't matter much I guess.
At this point it's a good idea to have a friend on the outside ready to catch the screen, or attach a twin suction handle on the inside so you can hold the glass while you push the rubber out.
so now you or a friend have got a good grip on the screen apply pressure evenly over the top half of the screen, this will ease out the sides until the screen is free to lift off the bottom lip, do not apply pressure only in one place only as this can cause the screen to crack, you kind of have to get a feel for it, use your judgement and take your time.
So now the screen is out, clean it. completely. Remove all traces of sealing compound, silicon, and whatever else has been smeared on it to prevent leaks, you want a good clear dry screen to start with.
Also clean the aperture completely, remove all black sticky goo and everything else, but if you can, leave the headlining in place, if it has come unstuck, glue it back down, or you will crease it up and it will look rough. everywhere else you want good clean painted metal to ensure a good seal.
So now you have your nice clean screen, spray it with fresh detergent/water mix. Grab your new rubber out of the bucket and offer it up to the screen to make sure you have it the right way round etc... Then starting with one long edge, usually the top, push the rubber into position and gently ease it on working down both sides of the screen and along the bottom, don't be afraid to spray it again with the soapy stuff, you don't want to force it, it should just ease itself on.
Now back to the car, to keep the screen in the right place and to prevent it dropping in the aperture you'll need some flexible putty sealer, I can't remember its exact name, or where to get it, it just fell off the Autoglass van whenever I needed any
... anyway it comes on a roll and you'll need to put it all around the aperture, take it off the roll an knead it until its pliable and then stick it to the lip where the panels join, smearing it into the radius of the aperture, double it up on the bottom edge, as this will take the most weight.
Back to the glass, you'll need either a 'string-in' tool, or a good long length of soft nylon rope, about 3-5mm in diameter when stressed (pulled tight) loop it around the rubber making sure it is in the landing recess where the screen aperture will be when the screen is fitted, this will enable you to pull the rubber through the aperture and seat the glass and seal properly, loop it all the way round and cross it at the bottom and carry them on to the bottom corners of the screen, make sure you have a good length either side, do not allow them to become uncrossed. now spray the rubber gasket again with the detergent spray, you want it wet.
Taking great care not to let it slip out of your hands, place the screen and rubber on the car resting in the aperture, making sure the free lengths of rope are inside the vehicle.
If possible get your ever helpful friend to have their hands putting light pressure on the glass, you don't want it falling back out at this point, it shouldn't, due to gravity, but if you knock it or something it might... if your friend has got bored and gone home, use the suction handle instead.
Inside the car, carefully take the two free ends of the rope and pull them towards each other, if all goes to plan they will pull the seal in and over the lip from the outside edges inwards. when you get to the middle they should uncross and continue outwards and up around the screen, across the top and out of the recess, you should now have the screen sitting nicely in the aperture with the seal nicely in place and a big loop of wet rope in your hands.
Back to the outside, gently push the seal outwards a little from the glass, especially at the corners, to seat it properly, you might not need to do this if all went well. what you want to see is no visible recess around the screen, with the screen sitting neatly in the seal. If there is a large gap anywhere, try to tease the seal into place with gentle pressure, if there is too much of a gap at the top you will have to remove it again and add more of that black putty stuff on the bottom edge. If all looks good, remove your rings if you have them, and firmly slap the screen to seat it properly, you are wanting to slap in a downwards motion, firmly but not too hard, try to aim for a 'wiping' slap rather than a direct hit, be careful, it is highly unlikely you will break the screen if you do this correctly , avoid hitting the center of the screen, rather aim for the sides top and bottom... be firm but gentle, again, it's a 'feel' for it rather than an exact science.
ok...this is getting long isn't it.... now it's time for the trim, this will put tension on the gasket and seal it properly. If you're using new shiny trim, warm it up with hot water, or a hairdryer, so it's pliable and start place it into position. If you're re-using the old trim...do the best you can with it....
There are tools for this next bit but they usually don't work very well and I find half a peg or a piece of wood cut to a blunt wedge works better, you want it the width of the trim, and you want to insert it into the trim recess on the gasket, so it spreads the lip out and press the trim into position. did I mention using the spray again? Spray it, get it wet and slippy, it will go in quite nicely. Do the bottom first, then work up both sides in turn until all the trim is in place, then fit the corners and top piece to lock it all in place, occasionally slapping the screen if needs be, you can move it around a little this way, it all helps.
If all has gone to plan you should have a nicely fitted and sealed screen. Now wash all that soapy rubbish off, dry it, and you're done
It isn't an exact science, you can have good ones and bad ones, even an experienced windscreen fitter breaks a glass from time to time...just be careful and methodical, you'll be fine
I think that's it, sorry for the long post but I hope it helps