1969 Spider Starter Motor

Occasionally, usually when hot after a run, my spider won't start. The starter motor turns, seemeingly weakly, but does not engage with the ring gear. Any thoughts as to cause and repair?

I assume removal is reasonably easy, though the carbs and steering box don't make access easy.

Could this be the solenoid not throwing the starter pinion into engagement properly?

Can the solenoid (appears to be held by two bolts) be removed for cleaning?

any help welcome..

Jonathan