You are going to need a new grommet no matter what; it's so hard by now it's not going to be sealing well at all.
Also, I personally wouldn't worry about the CDR - the CDR is supposed to be wide open 99% of the time; the only time it closes is if you somehow manage to clog the air filter badly enough that the engine starts drawing a significant vacuum against the crankcase, at which point the CDR closes preventing a runaway(*).
These CDRs also fail open, not closed, so as long as you change your air filter on a regular basis you'll be fine.
(* Note that I'm still not sure you'd get a runaway even in this case - I sure haven't heard of it ever happening. The only way I've gotten a runaway IDI was with literally half a can of lightweight ether lubricant[after the ether evaporated into the intake] soaking the air cleaner. Once started and revved up to like 3K, it finally started pulling enough in to actually just burn that. Revved to like 4K+ for a good 15 seconds before coming back down to idle).