well thats just silly.. guessing you dont service your engine then as it runs fine?? (if it aint broke dont fix)doing it is called preventative maintenance
gearbox fluid brakes down just like anything.. and job isnt hard to to.. remove two gearbox pans drain oil swap filter replace gasket (x2) and replace amount of fluid removed with new fluid.. yes not all will be replaced but a good percentage will be (you can go further by using coller lines to drain system fully...) .. once this done a couple of times most of old fluid will be gone and gearbox will be thankful for it and should make a much smoother box..
my dad left his never having it done from buying it at 70k to 120k i persuaded him to do it .. wasnt expensive
and drives so much better .. gearbox better when cold and smoother. on a 132k now and going to do it again just so more of it replaced and add a little lucas oil modifiy for autoboxs
If it aint broke and works as it should ...leave well alone.
Its a messy nasty job so I would be in no hurry to venture under there