Stripping the plastic out?
If you put too tight a spring on, it seems to eat away the ring that rests on the backplate side. You want it tight though.
As for doubling up, if he keeps blowing through them, its sounds like there is space to fill to me. Only because hes going through so many. Those two parts vibrate violently, and the slop can allow it to rub horribly if its not a snug fit IMO. Depending on the header make/size and gasket thickness, it could be possible.
I'm just tossing grenades at a problem I havent encountered. Not on that scale anyhow.
For all I know, it could all be wrong.