Yes, know all about PTFE and silicone hazards. I have a spray booth and masks that I use for another hobby.
As for old vs new string beds I had read that even silicone must be reapplied with use. And while slippery I don't believe it will stop the 4G crosses from denting which is a completely different issue. So it needs to work whether the 4G is fresh or dented.
Only on Talk Tennis can you find people who believe
that 10 feet of lead tape has no effect on a frame...