Clean soft extang tonneau?

[BIGt0007]

Guys, I got a lot of muddy spots on my extang soft tonneau cover. tried the power wash, then clean with a multi surface cleaner method with no success. can't get the spots off any tips?

 

[IRONMAN]

Try WD-40, or GOOF-OFF, or OOPS,or OXY-CLEAN(turn it into a paste).
Now try these things in a small area to make sure they don't discolor and of coarse not all at once.
Just ideas.