Causes of blue smoke on start-up of 1966 MGB. Valve stem seals?

[Dirk de Boer <deboer@duke.usask.ca>]

The last two weeks my 1966 MGB has emitted a blueish cloud of smoke on 
start-up. The engine starts up right away, and there is no smoke on 
acceleration or deceleration. Also, it seems that there is more smoke 
if the car has been standing longer.
My first guess is that the valve stem seals need replacement but I 
wonder if there are any other possible causes.

Also, my MGB (serial number 85,xxx, I forget the exact number) is a 
1966 registered as a 1967. I think it was first sold in 1967 so 
that 1967 is the year it was first titled.

Dirk