Yeah, figure Ace would have them.
I used to see them regularly at Eagles and Lowes.
I think Home Depot also has them in the miscellaneous fasteners section?
I think they are called "screw covers", or something like that...
They are used to cover the exposed threaded ends of screw when they stick out of things.
Hmmm...I've never had them crack or fail, even with the heat...
In fact, they shrink a little due to the heat for an almost custom fit.
I let the RTV dry overnight before having it handle a running engine, so there's no problem of it getting sucked into the engine.
Most fittings are close to an inch long, so it's going to take more than normal engine vacuum to get dried RTV out of them!
-Ted