David,

Believe me, it is possible to get a socket on the crankshaft bolt without pulling the radiator, etc.
I use my injector socket and a large rachet wrench to turn mine.

As for cleaning the timing marks, crawl underneath the car from the front and the marks will be right there in front of you (if the crankshaft is in the right position, otherwise turn it as above) for cleaning.

Hope this is of some help. Good luck.

__________________
Ted
1979 240D
165,000 miles