Hi. Was just wondering how you've fared in fixing this one?
BTW, I have a similar one, a MF40 industrial. Mine has a loader, but no backhoe although a lot here did come equipped with both. They have the Perkins 3cyl 3-152 diesel, but a 4.203 would be a godsend! I rebuilt the engine when I first bought it, and it's been fine since.
Yours sounds like it just has worn rings - pressurising the crankcase and pushing oil out wherever it can escape. If the liners aren't too badly worn a hone, rings and con-rod bearings would be the minimum. As stated - how's oil pressure warm at idle? If it's not extremely low main bearings should be Ok. As you said it starts well and pulls well; if there's not a huge presence of black smoke under load injectors should be Ok and don't even require removal, same for pump, camshaft and crankshaft.
The job isn't difficult. Again as stated, attention to cleanliness, a good repair manual and all filters renewed on reassembly - having worn rings particular attention to oil-bath air filter - and bedding rings with some heavy work ASAP after reassembly. That machine is well worth maintaining.
Good luck!
PS Can we see some pics?