Bought a new o76 in 1985'ish Benn*e and owned it to 2002 when I got an 066. Terrific saw the 076 btw.
Your post made me think back to its habit of smoking its ar*e off when first started after having been sitting for a while, testing the grey matter but I think a couple of weeks or more would bring that about.
It'd always start, but blot out the sun for a minute then totally normal after that.
I remember pulling the plug and it was very oily. All I could think at the time was if it was put away with a fairly high level of fuel the fuel was going into the motor and the petrol evaporating leaving the oil.
Your problem seems similar and it'll be interesting to see what you work out.
That saw also taught me that when checking the spark with the plug resting beside the plug hole for earth don't be surprised when the fuel vapour
ignites............
PS...thinking more, can also remember having to take the plug out to drain oil as it wouldn't turn over due to oil above the piston. Be good to find out.