If you are that attached to your 240D, then I wouldn't quibble about getting the necessary shop work done to find out the problem. Perhaps you will need a new engine, although that seems doubtful. I have an '82 240D with 381,000 miles on it, and I replaced the engine last year @ 375,000 on the original engine (I bought it from my brother in law @ 300,000 miles driven all that time in California over 13 years ago). the engine finally died and refused to start. My new engine (rebuilt from MB and shipped from Berlin) runs great with a 4 yr. or 50,000 mile warranty, and I spent far more than the car is worth, but I love it. So you should consider how devoted you are to the car, rather than agonizing over the particulars.

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DHB