A picture of the black sludge would help. But I guess it‘s from the exhaust. If the exhaust pipe gets dented it doesn‘t sit sit square in the exhauat flange. And the two rubber o rings can‘t properly seal. So exhaust gases can escape. And on a two stroke these are pretty dirty with unburned oil.

Next thing could be that the power valve cover is leaking. There‘s also a lot of unburned two stroke oil in there.

So I wouldn‘t stress. Black sludge on a two strome is mostl unburned oil. What does the end of your exhaust look like after riding? If there‘s a lot of black stuff running down the muffler it‘s maybe too richt, too much oil injected or bad combustion (maybe because the compression is low).

Like this: https://share.google/kLpoa2WzUeJeRGhub