Picking up a 2000 RC motor with 38,000 miles that needs a new valve guide seal. anyone know how hard is it to replace? or if I have to take to a shop, how many hours it would take? also anything I should know about a motor with that high mileage? Thanks in advance.

Valve guide seal (aka valve stem seal) or valve guide?
Valve guide seals can be replaced with the engine in the frame (although airbox, cam covers, cams etc. need removal).
Valve guides need the heads removed.

My 2002 RC51 has over 43K miles with no problems.
I've heard of RC51's with 70-100K miles on the engine.

I personally know a fellow with a Honda NT650 Hawk with 75K (120K Km) miles on his engine without single problem. He loves it.

I guess I'm gonna fix that problem and run that motor till it blows(which is not gonna happen cause its a honda). And I'm gonna keep my 03 motor with 800 miles as a spare or another project