Ron, I did look at your post and was not really sure how to approach it. Sometimes you have to experiment a little. If I had the problem, I would start with automotive tar cleaner and or mineral spirits and compared which worked best. When I got the tar spots off, some of the disolved tar would have gone into the cement. I would then wash with TSP and let it set wet for a long time, maybe an hour, to try to pull the residue out.
Believe me, if I was sure of a really good solution, I would have already given it to you. Henry in MI