Back over 30 years ago, I found the pump shaft a little rough due to, presumably, some leakage past the carbon seal and the bearings shot due to the housing being filled solid with hardened sludge. I replaced the seal with one made from a motor brush, replaced the oilite bearings (I drilled them out as they were too small - not the best way to do it!) and used an electrical cable sealing cover boot as well. This was obviously before the inter web and no spares were available on my side of the pond.
It leaked oil (as they always apparently did) but has not been a problem since. The tractor doesn’t get run much, mind. I am confident the repair will outlast me.