Gear box oil intervals

[Big_daddy]

Think its time for me to change my gear box oil, what puzzles me, how often are the oil changed?
This garage who mainly deal with clucthes and gear boxes say its not nesscary to change it unless it making noises or leaking.
My car just pass the 90k mark, so how many miles does the gear box oil changed at.
for example when pressing the accelartor in low gears then letting go can hear a slight whing sound (eg like revesing). could be ok but want to be sure.

 

[Jonny]

Just had a look in the book and there's no mention of actually changing the gearbox oil, only "check & top up if necessary" every 20k miles.

 

[Neil_Ireland]

I had my gearbox oil changed the other day, 36k miles on the car. I was getting grinding from 2nd-3rd at high revs, changed to redline mt-90 oil and everything seems to be ok now...still early days tho.