Wayne, I was planning to change the gearbox oil. Spoke to an old fella who does gearbox repairs in North London. Said it’s very rare he sees issues with these gearboxes unless they have had hard life. Such as trailing etc. He advised me to leave it alone if it’s working fine, as if it was to go it would go and oil change won’t help it. But get opinion from here too to see what folks say.
