Two of the pedals I have acquired recently -- my PQ-4 and, just today, my BD-2 -- arrived with them completely missing...
I've found an cheap and acceptable replacement for them from the hardware department at Home Depot, but still. Are they just prone to deterioration from footswitch cycling?
The screw cuts through them eventually. It's pretty common. The Boss grommets are a tougher material than normal rubber grommets, so don't be surprised if your new grommets start getting chewed up by the screw.
I�ve noticed that on my real old Boss pedals the grommets are of better quality, they are more or less intact on the late 70�s ealy 80�s. But for newer pedals I have bought several that have been in really bad condition. You can actually see that there is another quality of rubber in the old ones.
Some of my old ones has evaporated. The grommets on my PH-1 and SP-1 has become black goo. Maybe they've been in contact with battery acid or left out in the sun or something.