on two cylinders, is supposedly the only problem with a local 300SD (for real cheap). Are we looking at a full valve job here?

I had one "dead" cylinder...determined after a leak-down test. Rebuilt the head replacing the exhaust valves-seats-guides. Machine shop charged $350...mechanic was free. I would guess it is a $500-$700 job, depends on where you take it.

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1983 300SD 343K everyday car
1983 300SD 285K from junk yard-tooks parts from deer car- runs great. Brothers car.
1984 300SD parts car-Hit deer
1979 300D 175K non-turbo "Doctor"
1979 300d parts car

I have known people to own Mercedes diesels (in this vintage) for many years without ever realizing that the valves have to be adjusted as a maintenance action.

You might get lucky with a valve adjustment. Or perhaps the adjustment is so badly needed that a couple valves have burnt.

Ken300D

A burnt valve in a diesel is a condition that is somewhere between Rare and Non-existent. This is a condition that happens in a gas engine due to a lean condition.

To begin with, you should, of course, adjust all valves. Follow this with a leakdown test prior to any further action. If during the leakdown, you hear air through the intake or exhaust, then a valve job should fix it up. If, on the other hand, you hear it through the oil filler cap, it has a bad piston/cylinder/rings.

If it does indeed need a valve job, there is absolutely no sense in doing ONLY the valves that are leaking. A huge percentage of this job is removing and replacing the head, and a complete valve job may very well work complete wonders, so it is highly preferable to have the head done completely and thoroughly.

Good luck,