Years ago there was a product which was used by heat and a/c contractors. It was black and it dried very much like rubber and came in a small (maybe 4 ounce) tube with a nozzle type tip. It was sold by a plumbing supply store here in central Dallas. The stuff was designed mainly to be used with rubber grommets that were not the right size and it was very commonly used to protect where a copper gas line entered a heating cabinet or where wiring entered. The neat thing about it was that with a wet finger (spit or water) you could make the "skin" very smooth so that an artful user could make his work look like the grommet it was used with. Sorry but I don't remember the name of it. I suspect silicone became more popular it is possible this stuff is still made. You might ask your a/c guy.

If that stuff is no longer made, there is an alternative I have used to rebuild several rubber connectors, plugs, sleeves. It is sold by almost any hardware store and is called liquid electrical tape. It reminds me very much of the old a/c stuff but it isn't in a tube. It is in a plastic bottle with a small and nearly worthless brush attached to the cap. If you apply it carefully and smooth it before it starts to skin over (and it skins MUCH faster than the old a/c stuff) you can make it look very nice. It is resistant to gas and oil and heat doesn't seem to bother it and it isn't sensitive to UV rays either. The last time I used it was to make a replacement rubber sleeve for a lawn mower engine...the equivalent of their pcv system. The old one had cracked and split to the point it allowed the little metal tube to fall out. It gets plenty of heat, oil and oil vapors and for a while the gas tank was dripping right on top of it before I replaced the fuel line.

Hope it helps.
Jon

~ Jon
1952 1/2 ton with 1959 235 | T5 with 3.07 rear end