Check with your dealer about buying just the sealing gasket.
Philbert
The gaskets are typically not what fail. They tend to be fine. Its the twisting mechanism in the plastic caps. The little tangs shear or bend, or the plastic warps. No way to fix them once they are gone. They get loose, and you can fiddle with them for a while, but then they give out, and that's it. I have a few spares that I got from parted out saws. One of my 361s has a loose one now. Have to twist it in there 2 or 3 times to get it to seat right. Time to replace it. I have had those caps not seat right several times, and either dumped gas or oil all over on more than one occasion. Never happens with the screw-in types.
Also the old screw in ones rarely fail. There are several types. They typically get to the point that the slots in them are completely stripped out and the edges are worn down. Then you cannot seat them right. But that takes eons. Sometimes the threads strip on them and they leak, and they have to be replaced. They require a scrench to loosen and tighten in the field though, as compared to the snap in ones. I figure that I need a scrench anyway to keep the chains tight, so may as well have screw in caps. No way am I gonna go with the easy adjuster side plastic dial, as I prefer the tried and true dual bolt bar tightening system.