12.3 volts at starter, still won't turn

[Mendonsy]

In would agree with all the "failing under load" suggestions except that the OP says his solenoid doesn't attempt to pull in so there isn't any change in load.
The first thing that needs to be resolved is the 8.3 volts on the solenoid issue, then once the solenoid works that may lead him elsewhere.

 

[Deano]

Battery going dead....

Or at least half the problem!