Sometimes a strong solution of plain old dish soap in very hot water can surprise you, especially with a good microfiber cloth.
Simple Green is pretty good at removing grease too. Agree on the ammonia solution too.
If its really stubborn, a bit of mineral spirits, turpentine or varsol etc on a paper towel can soften grease enough to remove and usually won't cause any paint loss but same thing, use in a well ventilated area and test in an inconspicuous place first to be sure.
For sticky tar like stuff, some kind of alcohol like rubbing or isopropyl has worked for me in the past but again, same thing, try in test area first to make sure it doesn't react with the paint.
BTW congratulations on such a rare and beautiful find, especially a matched set!
Good luck