I believe the M110 and M103 are supposed to pretty reliable, and some claim as good as the OM616/7. I bet you'll have more difficulty diagnosing issues with the Otto cycle, though, but if that bug's yours, I'm sure you already know that.

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1983 240D 3.0T 4-speed manual, now sold

1989 Subaru GL Wagon 5-speed Touring Edition