I`ve had 2 over about the last 20 years, first a 862, 90hp, then a 572 70hp with loader, and a friend of mine has had 3 and still has one on a land drive forwarding trailer. Parts wise Browns of Liversedge, the importers I believe will supply mail order next day.
They are a very basic tractor, with most things worked by rods and leavers.
Starting wise, they start on 24volt, but when running revert to 12volt, lights blower motor etc, I had no problem with them starting winter or summer as long as both batteries are ok, if one battery is poor, the relay that swops the battery connections from series to parallel wont operate correctly.
Brakes, they are a dry disk set up, just about adequate for the tractor and small load/trailer if adjusted correctly, with a large trailer they will need a lot of leg pressure, trailer brakes are air, make a huge difference. Air brakes was ok for me, as my trailers are air braked for unimog. some dealers retrofitted hydraulic brakes I believe.
Cant say I ever had a problem with the keyway scraggs said about on the rear stub axle, although it made it easy to alter the track width.
The earlier one I had a 1986 I think it was, had a direct link from the steering wheel to box, the later one a 1996, had a more conventional hydraulic orbital valve under the dash and was better on the road the older 90hp.
Biggest problem I had was a head gasket, Browns supplied a new gasket with a modification.
Servicing was easy as all filters bar fuel filter are washable and reusable, fuel filter has a larger pre filter blowl with cleanable screen in so main filters last well, and most other repairs are simple as most items are external.
Some of the operational functions are a bit quirky, gears non synchromesh, doesn't lead well for multiple drivers jumping on.
Good on fuel.
If you want to know more give me a shout on pm
The front axle problem on the one your considering, are you/your friend sure its in the diff? I have heard of one with the bevel gears going to the portal axle part, failing.
The is a overload dog clutch in the propshaft, that could of gone or slipping and making a noise.