FWIW:

I have run Power Service Diesel Kleen for 5k miles. It just recently made the idle noticeably smoother.

When I bought the car 5k miles ago, it had a stuck open thermostat which I'm sure contributed to carbon deposits.

I had the intention of running LM but could not find it locally so I never did.

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1982 240D auto 152k
1984 380SL 113k
2015 Ram 2500 6.7 Cummins
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1985 300DT
1984 190D 5sp Euro