Hi, sixto, Jim Smith, joe p and euro 287, all others thanks for the reply.

Those OEM super copper core Bosch plugs were not carried by the auto stores close to my house. All they carried were either Bosch Platinums, AC Delco ...etc. Will go to buy Bosch copper tomorrow and put them on to see what happen next.

As for the cam's lobe surface conditions, they all look like mirror surfaces, no raise edges, not a single scratch markings on both of them. I remembered my mechanic kept spraying WD 40 around the valve cover and center fuel distributor areas --- he was looking for vacumn leak area.

For the compression and cylinder leak down test, I will let the pros to do those test as they have the experience, tools and correct procedures for doing it.

mbtjc mentioned the mercedesengine.net to me and I check it out today. Their head rebuilt price seems affortable -- $390 per head plus exchange core and shipping. It is worth to condition this option -- if those cylinder test come out OK.

Well, thanks for all the reply and I have to go. Good night and I will post what's the outcome next time.