Valve Guides

[Steve Ensch]

I am about to tackle the task of replacing my valve stem seals and guides on
my 90 5cyl 10v.  I was told to use the viton type seals.  The valve guides
they have for replacement are either regular or the shoulder type.  What are
peoples experience on replacing valve guides?  Are the shoulder type used
for replacement and if I find out that they were used previously do I have
to continue to use them.

Thanks in advance.
Steve