I've currently got my EJ205 engine (2005 WRX Wagon) in bits after what appears to be a head-gasket failure. I'm suspecting the gaskets have been replaced before as there's evidence of sealant being used which I wouldn't expect from the factory? The other suspicion is the thickness of these gaskets, as they appear to be thicker than 0.6mm, which I think is the standard thickness. Can old head gasket thicknesses be reliably be measured with a micrometer? I'm thinking they might get squished a bit when installed.
So if these gaskets are the thicker ones, that may suggest the heads have been skimmed in the past, so is there any way I can verify this?
I don't think I've got warping, so I'm wonder what's best to get the head surface in a good state for new gaskets.