5th gear snap ring (Not popout problem)

[Thomas Reynolds]

A couple of months ago I posted than one day my car when in 5th gear, while
getting on and off the throttle the shift lever would move about 1/4 to 1/2
inch. Nothing came of this from the list or forums so while it concerned me
greatly I dismissed as some advised as motor mount or shift bushings issue
(even though it ONLY did it in 5th.)

Fast forward to one month ago. Driving home one Saturday night and while
trying to downshift from 5th to 4th I found a 'notch' between 5th and
neutral which which jammed the shift lever. I immediately crammed it back
into 5th and successfully proceeded to run every stoplight and stop sign
home (as I only had 5th). When I got home (about 3-4 miles away), I could
wiggle the shifter profusely and get it over to the 1,2,3,4 neutral gate.
But go back into 5th and 9 times out of 10 it would exhibit the same 'notch'
problem.

So car sits until today, when I pull the tranny and take the cover off. Here
is what I saw (and theorized was wrong all along just did not understand how
it could happen.)
http://bellsouthpwp.net/f/t/fthomasr/5th/MVC-633F.JPG

The Pez candy shaped item in the lower portion of the pic, known as the
'Shift Insert', had slid past the 'Stopper' and caused the symptoms I
experienced.

I stood there and pondered what happened and then noticed:
http://bellsouthpwp.net/f/t/fthomasr/5th/MVC-635F.JPG
Which is what appeared to be half of a snap ring. I have not found that the
other half yet, but will wash the tranny out, dissassemble it and hopefully
find it somewhere in there.

There appears to be damage to the 'Stopper' seen here:
http://bellsouthpwp.net/f/t/fthomasr/5th/MVC-644F.JPG

I never have had 5th gear popout. The other gears appear to be in very good
shape. No visible wear or marring marks. There are shavings at the bottom of
the tranny, and they are from the cover seen here:
http://bellsouthpwp.net/f/t/fthomasr/5th/MVC-646F.JPG

Questions:
The cover concerns me greatly. My father's opinion is that while sustaining
damage from the Stopper it appears to be reusable. I know that some have
posted that there are several covers available with different tolerances for
shaft clearance. Is this the area where clearance is? Or is it at the very
end of the shaft and the cover, or indeed Stopper to Case area thereby
surely not reusing the cover?

Others have posted on the forum that the snap ring has broken on them as
well and suggest cryo treatment with replacement for strengthing (just the
ring). I see that the ring is a tolerance fitment piece and has several size
replacements from Nissan. How does one measure and order the correct one? If
the answer is to buy several to test, how do you know how TIGHT it needs to
fit?  Would cryo treating shrink the snap ring?

Thomas
'97 200SX SE-R
F-Max Stage II Turbo
Albany, GA