Manual Transmission Question:

My 94 Wrangler (2.5L, 4-cyl, approx. 140,000 miles) has developed a
problem with the manual transmission: It is making a loud rattle-y,
clattery noise in 5th gear. Fortunately, 1st through 4th, and reverse
are still OK -- so far.

My big question is whether there is any chance that this could be due
to something external or am I definitely going to have to take down the
tranny???

Other questions: Should I plan on routinely replacing the clutch and
the rear main bearing oil seal at the same time, or should I just leave
them alone if they look OK?

Also: Am I going to be able to find internal transmission parts at a
normal auto parts house like NAPA or AutoZone, or will I have to go to
the dealer ...... or should I just send out the entire tranny to some
kind of specialty shop? (I have overhauled transmissions myself before
-- but not recently. The last time was about 35 years ago, and in
those days the Chiltons or Haynes books used to include detailed
instructions, but I don't think they do anymore.)

TIA, john w. (jwallacq AT hotmail DOT com)