It is a pain to get at and from a DIY standpoint, it is a poor design at best. Once you get the thing out, follow Steve's instructions for cleaning. When I last did mine, I found the plastic piece itself to be clear. I sprayed about 5-6 ounces of carb cleaner doun the vaccuum tube leading to the collection box at the base of engine. My jiggling cap problem was solved. FWIW (in the event you have just changed your oil), I had just changed the oil prior to doing this, and asked a friend (certified mech on everything from lawnmowers to 18 wheelers) if I needed to change the oil again. He said that little amount in brake cleaner in 4 quarts is not enouth to do any harm.

Good luck.
Hope this helps.
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D.P. Mulvey in Central VA.