other issues?
If a '91-'92 5spd NSX transmission has a manufacturers serial # that falls into "snap-ring" range, it will fail at some point due to a production faux plas.
However, NSX's outside that range of transmissions are 100% immune to snap-ring failure as that small metal 'ring' on the upper housing of the transmission was corrected. I am not sure what you are referring to when you say documented snap-ring failures in NSX's out of range? A transmission w/o a snap-ring can't fail due to something it doesn't have!?!
You should know that there is a preventive fix for snap-ring range NSX's... replacement of the upper-transmission housing will correct the problem. The cost for the parts & labor can near $2k. Sometimes it's good to combine w/ a clutch replacement or JDM-gear/R&P swap.
I'd think it's fair to say you can negotiate $1.5k from the asking price just based on snap-ring.
Other determinants of the NSX's value will be: *mileage, *service/maint' history, *aftermarket mods' (wheels/stereo/body-kits), *vehicle/title history, paint & body condition, seats/dash & interior condition, and if there are any issues w/ the a/c, stereo, or other electrical/mechanical/technical shortcomings.
Goodluck.