Just read this and as said ideally you need to get some miles on it to help bed the rings in.
But before you do that i would suggest ditching the millers running in oil and getting some cheap 15w/40 mineral based oil.
Also i definately would not blank off where the pcv valve is as that will just add to your issues by building up excess pressure, a car needs at least 2 seperate breather points to function correctly so would definately fix the pcv issue or blank the pipe to plenum and fit an atmospheric breather on rocker cover where pcv would be.........if its knackered knock the valve out of it so its open and put a pipe onto it with a breather filter, then take car out for a proper drive.
Leaving it running at idle in a garage will do it no favours at all.
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