You can buy tar remover or a bit of petrol on a rag .Try a bit on your paint work where you wont notice it first just to make sure.
I did exactly the same the other day (under seal),forgot to clean the gun out and the can popped.Luckerly i had put a large sheet of plastic down first but got a bit up the side of the van and I was covered in it.Used thinners on my self (no petrol) and you can,t use it on the van
I think mine was from new and where It had rotted out Ive replaced and covered it with 3M Body seal.Not every ones choice of coverage but it sticks like "**** to a blanket" :lol: .And where it haden't rotted I scraped most of the under seal off and it was shiney og paint underneath.So my guessing is if its protected it for 37 years it can't be that bad