I assumed that water did something to that piston because I was getting exhaust fumes in my coolant. this was confirmed today when I pulled the head and saw carbon buildup on the head gasket water passage seals. so I assume that prior to being started (when this all occurred) water had breached that piston somehow.
the #6 intake valve appears to be bent -- it should be fully seated at 6 TDC correct? if so it is not. when I pulled the head there was no visible foreign matter whatsoever. whatever had broken loose in there had either completely disintegrated or is hiding behind the exhaust valve. (no metal bits, shavings, etc) the piston itself had scrapes and scratches (lots of them) but nothing that would warrant it being replaced. I did find some watery oil in 5 and 6 but not a whole lot. I will post pictures of both the piston and the valve squish area of #6 soon.
so right now I have a bent intake valve, a scarred up piston, and no idea how the hell it happened. btw, head was pulled not long ago so the gasket was new, valves, guides, seals were all done. the gasket I used was Elring OEM, and it looked just like the one it replaced. it must be a POS because I heard that MB has made 3 changes to the m103 head gasket since original production.
I will be using whatever gasket the dealer peddles ... anyone know what brand they use, if not their own?