FWIW ended up putting up on stands, filled the transmission/gearbox with kerosene, ran in low and reverse for a few 5-10mins - no load as up on stands. Drained, no metal bits or filings etc - but decent amount of black/soot etc. Used compressed air to blow as much of the kero out as possible, filled will Penrite 85w-140: https://penriteoil.com.au/products/gear-oil-85w-140-mineral

Seemed to run smoother than before - but likely placebo effect.

Cheers.