smoking engine

I have a 2000 Chevy Metro 1.3l with 100K on board , the engine runs with no problem but at start up a plum of blue smoke shoots from exhaust, but only after the engine was siting overnight or after at least 5 -6 hours betwen starts, or after the oil is older than 2000 miles, during engine operation no smoke can be seen at tail pipe only during start up.
So my question is what causes oil to leak inside cylinders betwen starts?
My hunch tells me that I have bad valve seals but which ones? exhaust or intake ones?
The car has power as I said and runs good, the spark plugs are not fouled or with deposits so it has to be an oil leak.
I don't remeber our engines having problems with valve seals so what gives?
Any ideeas are greatly appreciated.
Thank you.

compression OK when cold vs hot?

Might be your valve guides. Check inside of your air filter for oil, if there is any you might check your pcv valve.

PCV valve is new with no oil inside, plus it makes no sense after 5-6 hours all the oil is drained from the head so it can t be in such a volume to be sucked by PCV.
Compression is ok across the board.

Pretty indicative of valve seals gone bad. Not to bad with the right tools.