Once the machine burns off what in the muffler or whatever it seems to stop smoking.
If it was oil rings it would smoke constantly no? Although oil r is more likely with 700 hours only if you throw piston rings or do any work inspect for fit and pliability/change the vss is an excellent idea also to determine where the failure is/was.
It is very important for you to post your results once the problem is solved so that people will be able to reference a solution to their problem down the road. YEARS may go by and someone has the same problem PLEASE POST YOUR "IT WAS FIXED WITH x SOLUTION.