I bought my Nuffield as a works in progress. Previous owner said water is leaking into the sump. They changed the head gasket and it still leaked. Now I am no mechanic but this lead me to believe it has something to do with the age and it being a diesel. I begun thinking it was a liner leak as my brother pointed me towards so now I looking to overhaul the engine. Finding a UK engine parts dealer I have since found out it has a later model engine 4.98NT and needs a different engine rebuild kit. Luckily the UK firm are on the ball and have not sent it yet until all queries are answered.
As to the tractor, I think its age means it was built to last and I like nothing else than to keep the old one's going and not end up in a ship heading off shore as scrap.