Hi all, can you give me an assessment of these compression numbers?

1 - 300
2 - 290
3 - 310
4 - 320
5 - 220

Check done on a 1983 300SD with 350k, cold (70F) engine, US General tester via injector. Valve clearances all checked & adjusted before. Fully charged battery with assist from charger.

I ran the check twice after I saw #5. First time I went 1->5, then charged the battery for another 3 hrs, and ran it again 5->1.

I added oil to #5, but couldn't get it to read above 220 no matter what. Pulled the valve cover and re-checked clearances, no dice. Couldn't spot any leaks, either.

Car runs well, but mileage has dropped since the last valve adjustment (~10-15k ago). Smoke has gotten worse.

All injectors tested good (Metro Diesel in Santa Fe using Diesel Kiki tester), so I think the smoke is coming from #5's low compression.

So here's the question.. is it likely repairable, and if not, think it would run another 50k miles?

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'82 300SD 351k