I never use those covers and never have gotten anything. If the rest room is flithy, I try to go somewhere else. I even used a disgusting port-a-potty in Rome, Italy because I really had to go and (thankfully) caught nothing.
(and it was nasty—I had to wade thru pee…ugh)
I don’t use the covers because they stick to your butt…I had one sticking out of my jeans once. Never again.
And, I’m waaaaay older than you, so it’s more than just luck!