Sorry I can't help much, I'm in the same boat as you. I have tried every way I can think of to clean my cap, but have had no luck. So far I have not found a source for new cap either, so I finally put a very small right near where the cap goes to be my vent for now. I'll figure something out later, or just plain get mad one day and rip the cap a part and find out what's wrong.
Travis