When I had some rust repaired/patch around the battery tray of my W123, the body guy used a fair amount of black, tar-like stuff, the kind of stuff you'd find under the car.

Not very pretty.

Although he admitted an error, he cleaned up as good as he could, I guess.

But like anything else, to do it right, you have to do it yourself.

Is there anything you'd use, to clean the fire-wall of this black, gooey tar?

Let me know, thanks!

If it's tar based, mineral spirits will work. If it's a PVC derivative then you're gonna have to use lacquer thinner.

Lacquer thinner has a low flash point so be careful with open flames and wear rubber, not nitrile or latex, gloves.