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I have the same year diesel with a rebuilt engine and 170k on it. From what I've learned on this website (Thanks Tom Bryant) using synthetic oil is the best way to go. He favors Mobil One but I found mine consumed too much so I 've been using Chevron Synthetic Delo 15-40 and changing it every 20k. i add 1 Qt of makeup about every 1500 miles. (Little leak at the oil pan gasket). This engine starts to wear at the top of the piston stroke on the cylinder walls and will demonstrate this wear when you run the engine without the oil filler cap. I also have a Frantz Toilet paper filter which I change every 3k. I've had the waste oil tested and the soot is always a little high according to the lab but I can see no blowby.
These engines do NOT like to be run hot. If you can't verify that the radiator was rodded in the past 22 years - better do so soonest. Another hint is on hills: don't let the engine lug and get hot- change down and rev up. Those are light weight pistons and can handle 4k rpm easily. On the flat at 70 my gauge needle is a little over the halfway mark and on the hills it will get up to about two widths of the needle from the red zone.
By now you've got the fuel filter changed but next time fill the new one with ATF to clean the injectors. Got that little gem from a VW shop.
Think ahead to the Cold Weather(You have cold weather?) Battery must be good. Original glow plug system relay sometimes fails in the ON position. You can bypass this with a dash control button. I have a block heater for the once a year run to Wyoming to ski. Winter and altitude are the acid test for these rigs.
Running these engines less than 10mi per trip guarantees a short life. They're best at cruising. You will be in the right hand lane on the hills (where the nicer people are) but you'll surprise 'em on the downhill curves (assuming you've put on IPD sway bars).
Last advice comes from Germany where they say not to buy a used diesel from someone who lives close to the Autobahn. This refers to the fact that lube oil doesn't warm up for at least 10mi and if you do high speed with a cold engine...