I have a Farmall 350 Diesel that I completely rebuilt several years ago. The problem I have had since then (and seems to be getting worse) is that when the head was reworked at the machine shop they didn't do anything with the valve push rod tubes that go through the head to keep them from leaking oil. Six of the eight leak to some extent with oil running down the side of the engine. I looked in the parts manual and they don't show any seals or o-rings. How are they sealed in the first place? Does repair require removal of the head? I took the valve cover off (not an easy task with the power steering unit overhead) and cleaned around the tops of the tubes and put a layer of gasket cement around the top of each tube and it stopped most of the leakage, but it is starting to leak more again. Any advice would be appreciated. Roger