So what if anything do you do, if you have a 92?
There is a preventive repair you can do. It was written up not too long ago on the NSX e-mail list, so I suspect Lud will insert it into the FAQ soon.
If I had a '92 with a transmission in the snap ring range, never shown to be repaired, I would do the preventive repair.
Was there ever a recall on the snap ring?
No. Failures were covered (partially or in toto) as goodwill for several years after the original warranty expired, but I haven't heard of them getting covered recently; probably depends on how many miles you've got on it, whether you're the original owner, your relationship with your dealer, etc. I wouldn't count on a failure being covered, but if I experienced one, I would certainly ask.