Jim,

It sounds like the tool isn't compressing the spring adequately. Isn't the compressor adjustable. If it isn't, can't you put a thin wood shim between the valve and the compressor finger, on the combustion chamber side to take up some room and allow for full compression of the spring.

Weren't the little stem seals the factory item? I remember putting umbrella seals on for added measure, but the stock stem seals worked fine if the guides weren't totally worn out.

If your spring compressor is adjustable, as it should be, you should be able to compress the valve spring until it is bound.

Stuart