It sounds like you are on the right track. If you found some dirt in the regulator then there is probably some at the filter and the needle valve too.

You obviously don't have a problem with the check valve yet but your turn is comming if you don't get a filter between it and the engine before long. I don't mean to quit using the plane. Just the next time you are procuring hobby parts, pick up one and install it.

Good luck

Jim