I have a 77 240d automatic and it was hard starting until I changed the glow plugs. Had never done it before but it was easy.

Found that one glow plug was bent badly, apparently by the mechanic that had changed them years ago. It was a little hard to get out because it was hard to get a wrench on it.

Anyway, it now starts immediately. Maybe one or two revolutions at most. It has a little over 213,000 miles on it.

This would be a cheap fix to try.