Change or leave gearbox oil?

[Ben93]

My corolla d4d 2 litre I've nearly owned a year and has been just fine. I'm getting the cambelt and waterpump and tensioners changed next month and was going to do the gearbox oil as it shares its oil with the diff. Now as the service book has stamps but no receipts of what was actually done during services I don't know if this has been changed. Cars on 77k miles and it should be inspected every 40k and changed if needed apparently. No issues with gears but I've heard that changing the oil on an old car that's not been done before can cause the gearbox to fail but other people told me this is an old wives tale. So is it worth changing or should I leave it be? I do intend on keeping the car I just can't fork out for a gearbox refurb or replacement. I've had one mechanic telling me the oil won't get dirty in the gearbox and diff and others saying it should be done.
Any help would be appreciated.

[Ben93]

I know it uses 75 90 synthetic might be worth getting it drained and refilled at the same time as the cambelt tensioners pulleys waterpump etc get a whole lot done and no. Got to worry in my time of owning it.

[Ben93]

Should be inspected every 40k miles or 4 years but I don't know if it's been done in its 77k moles and 11 year life but suppose no harm in doing it now.

[Ben93]

Will see how it goes it has no issues shifting or driving most people I've spoke to have never changed there geae/diff oil and there cars are on 200k miles on original box and some people who change there's don't make that. Depends if you go changing gears like a racecar I suppose etc etc.
I will have a look at the oil myself and see what it looks like if not too bad will change it if full of crap I'm leaving it be and not chancing fate. You know what they say if it's not broken. My engune oil is done every 5k miles though with oil filter etc. But that's a different story My first car I had I put 50k mies on it and it was on 160 before selling it and never had it changed so I suppose it's luck.

[Ben93]

Yeah normally when people go racing and don't put clutcj all the way down and it crunches into gears