Jay - as long as its within Merc specs (there's a sticker under your bonnet showing this) it should be fine, my mixture was over 10% CO, that's when you have to worry.

Warren I think the simply headgasket failed, it wasn't due to the head not being correctly held on. May guides are perfect according to the same engineer that the dealers use, as they should be having been previously replaced.

My engineer has informed me that my pistons are all 0.002" too small with piston number #5 0.004" too small. I now need to source some pistons for the vehicle. Seems strange that the pistons have worn and the bore hasn't though.