compression test the cylinders.... (if you were local to me i'd do it for nowt, can't wait until june can you ? )
that way you would get a clear picture of cylinder health.
Stems seals? Not a hope at that mileage!!! they are having a girraffe!
I have noticed with the older 12v Alfa v6 units, that if a cylinder missfires due to ignition/fuel related issues, it WILL give a haze of blue smoke under load!! (my old engine did it, and on start up)
Get a third opinion before you let someone tear into that motor