I am having something similar, but no garage involved.
K74 Diesel 4WD, head gasket problem getting exhaust gas into the coolant so I replaced the head with a new cylinder head from Milners along with new bolts and gasket. Did all the belts, pump, remove EGR at the same time. I know I did the bolts correctly in 3 phases as per the instructions. I have done head gaskets (and everything else for that matter) on cars before.
I guess the gasket was done previously but must have been quite a while ago judging by the amount of crud built up everywhere. The water pipe to the turbo was actually completely full of crud, surprised the turbo hadn't gone pop. The gasket I took off appeared to be exactly the same as the one supplied by Milners.
Started it up this afternoon and now I have water seeping out of the head gasket just below number 2 fuel injector so really confused by this. It was not doing this with the old head and gasket. What I did NOT do was check the straightness of the block. All looked fine and to be honest I just forgot to get a ruler on it. It all looked OK and it was clean and dry.
So now I need to take it all apart again, the suspicion being that the water must be leaking from the waterway between number 1 and 2 somehow. Would like to hear any experiences with gasket sealer like mentioned in this thread. The intention would be to only apply it in the affected area below number 2 fuel injector. I have K&W Copper Coat which I have used on all copper head gasket for american V8, but not sure about using it on a composite or Multi Layer Steel gasket.
Thanks for any input both on gasket sealer and best gasket to use.