Valve Stem Seals

[pgackerman]

How far down should the valve stem seal go over the base of the valve stem?

The seal is shaped like a cap, and the stem base looks like the seal should go right over it all the way down to the cylinder head.

From experience I can tell you the seal does not slide all the way over the base and touch the bottom of the cylinder head.

[Fierofool]

It sounds as if you have deflector style seals.  They move up and down with the valve stem and just keep oil from running down the valve stem and being sucked around it during the intake stroke.  Positive seals are affixed to the stem boss and do not move.  Maybe this how-to will be of some help.
 http://www.fiero.nl/forum/Archives/Archive-000001/HTML/20090907-2-089685.html