I've never had much luck chasing voltage around when you are dealing with a high amp device like a starter.
Solenoids can have very burnt or corroded contacts and still read the correct voltage but do not have the surface area left to pass 50+ amps of current.
I prefer to jumper around the solenoid with a heavy duty jumper cable to see if the starter itself is good. This is ONLY after checking the battery and all connections and cables to insure that they have the ability to provide the amps necessary to energize the starter.
When running a jumper to bypass a solenoid I prefer to hokk one jumper up to the connection on the starter, and then use another jumper cable that is connected to a battery. When everything is clear, I would then touch the two ends of the jumper cables together while I was not under the rig.