My local rubber supplier has a boot seal that almost works but doesn't have the tiny 3mm deep slot that goes over the lip. The one they stock is sourced from Scott's old rubber in oz. see 260.057...
http://www.scottsoldautorubber.com.au/page16.jpg
But it does not have the little slot that would hide the metal edge.
Any ideas? I have had a quick look on woolies but no luck there.