Hmm, I suggest you get another mechanic. Or at least get him a copy of my book!
This is a common problem on these engines, the plastic inner tube cracks and then breaks, leaking oil near the coils. The parts you need are a new spark plug tube and o-ring (some brands come with the o-rings, some do not). The part number is 996-105-325-52 and you can order it from the Pelican catalog here:
http://www.pelicanparts.com/cgi-bin/ksearch/PEL_search.cgi?command=show_part_page&please_wait=N&make=POR&model=986M§ion=BAStun&page=1&bookmark=3&part_number=996-105-325-52-M127
- Wayne