I think I mentioned this in a pervious, but I initially put 10W40 engine oil into the gearbox accidentally. Have realised my error I initially just asked around to see what other people thought about just leaving it. Alan made a great point, that when I change it shortly it’ll have cleaned out any debris that might have gotten into the gearbox while it’s been stool for the past how ever long in storage. So I pulled out the sump plug and found this.
So it either wasn’t 100% clean inside or the wrong oil caused a lot of wear or it’s wearing really fast and will fail at any moment.
So I made a but of a mess on the floor, but the job is done, 80W90 now in the gearbox. Still not exactly the right oil, but I’ll live with it.