Bounce sheets. Or any brand dryer sheet. They take pine tar,bugs,caked on carp off pretty easy so road tar isn't much of a stretch from pine tar....right?
Engine starting fluid(ether) may help. Isopropyl alcohol maybe.
Carb cleaner spray should help too.
More than 1 way to skin a cat.
Stoner Tarminator if you haven't tried that yet, it's just plain works as intended...on TAR, or when I run out of that, it's xylene/xylol mixed with mineral spirits (of course, I live in CA which banned xylene/xylol). If the tar is dried and hard, nothing is going to make it an easy quick fix.