Yes replacing the entire regulator is the simplest. It has been my experience that rebuilding is very tedious, due to the fact of getting the plunger to seal on the seat properly. This must be done, and tested while regulator is being reassembled and once you find the sweet spot you actually have to glue it in place. You may have noticed that the factory was glued as well.
The fuel can definitely create some major issues. The grade of propane you are being supplied can drastically differ in the amount of propylene contained with in it. Propylene is the black stinky sludge that came out of your regulators. Ask your supplier what grade of propane they are suppling you. It is best to run grade HD5 if possible (don't be fooled, HD5 is better quality than HD10). Another to consider is if the contaminates that you got from your filter housing are rust colored. If so are you running steel fuel tanks or aluminum. Best to run aluminum.