[Tuffty]

When they tap it's nomally because they get gummed up with debrits from old oil, doesn't harm the engine, more of an annoyance than anything.

As for fixing sometimes a couple of oil changes can cure them, if not they can be removed and cleaned http://www.lancerregister.com//showthread.php?s=&threadid=18708

failing that you can buy new ones with a slightly larger filling hole from various companies on this forum as stated above