my car has a rubber plug for an oil cap in the valve cover & it's a pain to get on & off, is it possible to replace it with a screw on type without swapping the valve cover, & what vehicles would i find one?

Just go down to the local Auto Parts store and buy a new one that's still squishy, that's what I did.

Yep for about $6 you can get a uni one thats chrome n says oil on it. It will have a long rubber end kinda of with several different steps. You can cut it down some so it fits yours better. They make it like that on purpose .
So it fits almost ever cars oil hole.