Oil leak on EC300 expansion pipe

[colinmc400]

Guys, got one ride on my 06 ec300 having just had the piston and rings done, as well as lots of other planned maint type stuff. I notice there is oil leaking from the flange the front pipe mounts onto, on the front face of the cylinder. Did i read on here that one of these holes is not blind and needs sealed when the bolt goes back in? I also get the impression that that mounting spiggot/flange that the pipe slips onto can crack and leak(as i see Nth Tahoe m'sport offer a ss version). Any ideas would be welcome before i tear it down.

Sorry one is a bit blurred, but its the bolt at the 3 oclock position. I have added a couple of bigger pics in the gallery.

Any comments would be greatfully received.