I am having a problem with my Antigua A535-LQ

Good (evening, morning, afternoon)

I had to take all my Martins up to Chadd to fix some minor (mostly) repairs, so I broke out my Antigua A535-LQ. It's from 1998, so it's almost vintage! When it works I like it OK.

Right off I had to take it in because the G# pad was leaking making notes below "D" nasty. The little bumper thing that holds the G# pad down had broken off so it wasn't sealing.
This was back in January. They replaced it and the horn was OK. I am pretty sure they put in a little bumper made out of cork.
In February I had to take it back for some other stuff they didn't notice the first time, even though they went through the horn and found other stuff to fix.

So tonight I can't play low notes again on that horn. Just to make sure it's not my crappy embouchure, I get out my backup backup horn, an Antigua A525-LQ. It works OK.
I got out the leak light and the G# pad is opening when I play C, B and B flat on the 535

The danged little bumper is gone again. It looks like it broke off, so it lasted about 3 months.

I looked at the 525, the bumper thinger looks like it is plastic. I found a horn on the junk pile that also has a plastic piece there.

So my questions are:
1) should a cork bumper work in there, or should it be some other material like plastic or felt?
2) if cork is OK, how long should it last?
3) do I need a better technician? (this wasn't Chadd)
4) do I need to abandon these horns and buy a new Kessler?