Take the head and have it professionally checked for cracks. The 603 is not known for blowing head gaskets. It is, however, known for cracking 14 heads. Mine has been fine so far. They not all bad, I am the first one to say that. BUT, they are not known to blow head gaskets like the 602.

Good luck.

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08 R320 CDI current

Past
95 E420
87 300D Turbo 5spd
90 300TE
83 300SD
85 300TD
92 400E
85 190D