yea sounds like gearbox oil, what's mileage difference ? i would use opi oils to rate the gear oil needed as there pretty dam accurate, the gearbox oil when people ask about changing it, all the manufactures say its "lifetime of gearbox" even some third party garages say same its a load of crap, you'll just blow the gearbox as the oil will be like treacle or contaminated, that's why you see allot of dedicated gearbox rebuild places around, and your starting around 1k for that rebuild.
was talking to a guy id not seen for years other day and he had a vw transporter camper with 350k + on it and was asking his local garage as it was stiff changes and they said its lifetime, well one of the gears went after that and that was fixed and replaced oil he said its been smooth since..
I got a spline bit kit off ebay a while back as it was needed to replace the door locks and not bad quality , there not all that dear, if you done your own locks you might have a bit that fits