With a new radiator I might wonder if it had been overheated in the recent past. Overheating seems to be hard on a lot of gaskets throughout the engine. Ask me how I know. I concur on the h.g. when my hg went south, the car ran rough and noticeably smoked blue black. As noted, it was the gasket between the first piston the the chain galley that failed. I was able to replace the gasket myself. Not that hard if youre patient.