Now this is a question i found allot, but pittily the answer that i found multiple times doesn't seem to apply to my problem:
I read multiple times that this is usually due to the normals pointing the wrong way, but it seems that isn't the problem!
Also it might be worth mentioning that trying to flip the normals in that part of the object (although that should turn them to the wrong side up) causes them to be black and unpaintable, while now their untouched neighbours tend to be white and unpaintable! (no picture due to lack of reputation)
Thanks in advance for your help!
As you may have guessed this object wasn't modelled as one object in the first place, but joined together for the purpose of being painted on and exported. Due to the format i wish to export this to (and the fact that this is merely an experiment) the solution of trying to paint them separately would only be my last resort.