Before you do anything, check belt tightness and charging voltage. If you pull on the belt forcefully and can make the belt slip on the pulley it's too loose. Should be above13.8 v charging voltage. A loose belt, bad alt/ v reg won't give you that. .

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85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked