I concur to have the lab check the gas content in the oil. If the amount is small, and you get the car good and warm I would think it will burn/ evaporate out.

The spluttering might be it getting a little extra fuel on start up. My sec did that for years with no ill effect. The color of the plugs suggest its not a problem that continues after the start up.

If the cold start was staying on it wouldn't run right after it got warm, IMHO.

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.