I had the same problem with my old 240D. The problem is with the starter (it was sticking), especially if you have the original one in there after all these years. I replaced my starter with a rebuilt one (cost around $120). I don't know if the starter has a solenoid. A trick to get the starter to turn is to contact both leads on the starter with a screw driver while the ingnition is on. Make sure the car is in park or neutral and dont stand infront of the car. You should hear the starter turning. Hopefully, it will turn enough to get unstuck so that you can start the car using the ignition key. Good luck

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'82 300D Turbo 216k miles