Hm.. So this is how that sol invictus locked like? - I have one Rome minted in a lower grade where the Sol is not quite visible: In Constantinople at the Forum of Constantine there was once a column with a bronze statue of a naked Constantine depicted in a similiar position: Here Emperor Marcian(Eastern/Byzantine Empire), this statue is now in Italy(taking from Constantinople after latin sack in 1204 if my mind serves me right), but unlike Constantine he is shy and hide his sausage:
Well, that is true, perhaps i should have added it. - We don't know for 100%, but a lot suggest it is Marcian giving that Marcian was a giant as a person(just as the statue) But you are right that we don't know it with certainty.
To the OP: If you must clean an ancient, gentleness and patience are best. Acetone, distilled water, and a gentle solution of ammonia and water are your friends. Way to ruin a coin man. Sure,it's for you, but when you die the next collector that gets it will have a purposefully damaged coin. If you must use that car grease stuff, I'd rather you stick to collecting horse shoes or something of the like, and not ancient coins.
If any of you got it yes you might think it's ruined. You also might think what a good looking coin. I'm tempted to give this 1941 half the treatment. But the reverse looks scrumptious as is! I have to get more 50 cent and larger flips. All I have now are quarter, dime and penny size.