Having a similar problem with a 370Z I just acquired rather cheaply that was using a bit of oil on no1 and blowing smoke on start up and had high misfire count on no1 as well as a result. I had hoped that it was a valve stem seal and might be easy to fix but now don't think it is. Compression is still pretty good so think that it is a gummed up oil ring ; as in my experience it is rare to break rings now days and the car had a very poor service history. I soaked overnight in lucas oil additive and it did not do much and then tried overnight with Marvel Mystery oil and improved a bit and then tried a concoction of wynns, nulon and no name brand cleaners. I could not find Seafoam here in Australia but the Nulon hinted at being similar. The top of piston and inside seems pretty clean now when I put a bore scope down the plug hole but sadly problem has not disappeared but has improved somewhat. I was doing an oil and filter change after each of these treatments along with an engine flush. Am just going to drive a bit for now with no more engine flushes and try some valve/ engine stop leak /additives and drive it for a bit and see what happens.
