Thanks for your help. If the tensioner uses two mechanisms to tension(mechanical and hydraulic) then I suppose it is OK if it retracts a bit with the engine off. It also explains the gurgling noise. I can see the sliding face of the tensioner and it doesn't appear to have excessive wear at all. Does the chain ever develop a tight spot in it? That might account for the "bump" I feel in the slider with the engine running.
As I said earlier, everything that I can think of checking looks good on this. I was hoping for the "magic bullet" effect today, where I get a bunch of responses saying "check the _______!! they make that noise all the time!!" But after not finding anything with a search I should have known better.
Leathermang, thanks again for all your help. I'll double check the chain and put it back together. My 1100 mi/week commute will surely make the problem obvious soon enough (unfortunately at a higher price tag, usually). I'm done fooling around with this. I've got too many hours in it now...
Joe

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1978 300SD
Running Biodiesel/SVO, 2 tank system
127,000 Miles