Norm,
that's all I needed to hear to convince me of the difficult path ahead should I attempt a repair. I'm running the white flag up the pole as we speak. It has defeated me.
I think that the hole has opened up enough that unless knurling and loctiting could secure the gear unit, something along the lines you describe would be necessary. And that isn't feasible.
Unless AVB thinks there is a chance of knurling working given the hole enlargement described, we can well and truly say RIP engine.
I'm considering another Greenfields as an immediate and cheap replacement, and if it fails I will fit one with a Chonda. Plenty of spares if I buy the one I'm thinking of because same unit- frame, body, deck, drive, just with a 17hp motor. And I've now developed a level of knowledge of the drive and other features, it seems a pity to go to something with a drive system I don't know anything about. It will hurt to part with over $5000 on a new mower that could do the job- a club cadet tractor (XT2 LX42) or zero turn (the RZT S series) are the recommended units. Happy to hear anyone's opinion on these mowers.
I suppose that about wraps up the governor issue anyway.
Norm and AVB- I salute you.
Cheers