i recently had my front pipe changed on my 2001 e39 530d for a stainless decat one. At first it was noiser but settled in ok. A week later my turbo blew and lost power. My "mechanic" changed the turbo and also deflapped my swirl flaps at the same time. After 900 miles and a trip up north i got home with no problems. Next day i heard a rattling sound from the top of my engine to the bottom followed by a missing on one of the cylinders.Next day my "mechanic" had all the injectors checked and they were fine. Next he took the head off to find no1 piston had a dent on it and the head was scored on no1. He says he has no idea how it could have happened. My other friend reckons he never cleaned out the intercooler properly when changing the turbo and this bit is what has gone through and damaged th piston. When he changed the piston he checked the oil pump and this too was badly damaged inside and i had to change this too.Can someone advise me? do you think he never done the job right when changing the turbo etc.The only other thing i can think of getting into the head would be a valve guide but he says there was nothing in the sump when he took it off.I just dont know how something can get between the top of the piston and the head any ideas please guys?