Deszus, ill give you the FULL back ground story of my SB3 under my ownership.
im the 7th owner, had NO service history that came with it although i knew it had had an oil and filter change before the 6th owner bought it. when i got the car in November 2015 it had ticked over to 83,000 miles. as a result i figured next service ill replace all the fluids, the service light came on in February 2016 and serviced the engine. a few months later i replaced the gear oil and added some liqui moly gear oil additive, as i didnt know how the previous owners looked after it or drove it.
when the oil was drained it was a little dark but i wouldnt say it was sludge like.
in early December 2016 it had done around 92,000 miles and i replaced the clutch, yet another gear oil change was done as when i removed the drive shafts i lost a lot of oil (looked like the same viscosity when it flowed out) and topped up with some oil that i had got from the local motor factors.
i wasnt happy that it has 2 different makes of oil in it, so a week later, replaced the gear oil. again no difference in viscosity from the previous 2 times.
in November 2017 the gear box started getting noisy and mid December the gear box was replaced.
in the space of 2 years i replace the gear oil 3 times on 1 gear box.
i have bought more gear oil for my forfour than engine oil... an expense that i could have done without.
as iv mentioned before Deszus stop having a go at others for not doing what you are doing to your forfour. iv seen Jags go for over 150,000 miles on the same gear oil, i replaced the gear oil on my uncles civic at 195,000 miles when i replaced the clutch, so you cant say gear oil should be changed like engine oil. engine oil and gear oil work in different environments. gear oil works in a 'sealed' environment where contamination isnt possible from other sources, where as engine oil can become contaminated by fuel. as a result the engine oil HAS to be replaced yearly where as gear oil can effectively be used for life. yes, replacing it will do the gear box good BUT at the expense and time which most wont want.
