Besides the duff solenoid output I've also had intermittent starter operation that traced back to the under tank relay. Tested good with a meter but wouldn't flow enough current on demand, you can find an exact replacement for around $12 at O'Reilly's auto parts.

A positive attitude may not solve all your problems, but it will annoy enough people to make it worth the effort. Herm Albright (1876 - 1944)