Check the Oil Cooler hoses and if there is any seepage change them. However, the Oil Cooler nipples are aluminum and the Oil Cooler Hose Nuts are steel. That often means the Nut is corroded to the nipple and when you turn it strips the treads off of the oil cooler nipple. (That happened to me.)
Look in the Repair Links for ways to decrease the chance of that happening.
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The driver shaft has rubber flex discs on each end. Check both ends for cracks even though it is not as easy to see the front one. On the ones with automatic transmissions if the front flex disc comes apart it has been known to crack the whole tail end off the transmission.
Us only Bosch or Beru glow plugs. Do not buy Autolite Glow Plugs. Myself and others have had the tips on the glow plug swell. In my case it only took 6 months.
See the attached picture. If you already have the replacement oil cooler hoses one of our members said it was possible to (see the yellow line) cut the oil cooler nut length wise in 2 spots on opposite sides and stick a screwdriver in the slot and split the Nut. That avoids the turning of the nut that strips threads off of the nipples.
The oil cooler hose seals inside of the oil cooler nipple not on the threads so if the threads get a little dinged it won't make a difference. However, no one I know of has cut the nuts as suggested.