Jim Levie wrote:
The unloader doesn't stay open after cutoff. It opens to relieve head
pressure and then closes. ...

Mine doesn't. Mine is opened by the armature of the pressure switch.
As long as the pressure switch is open, the unloader is open.

The start switch should not be doing "a lot of arcing during start". ...

No kidding?

... the start cap. They do weaken with age and are
temperature sensitive, ...

Ah! That is consistent with the symptoms.

While is possible that the counter balance springs in the start
switch have weakened, allowing it to open early, that's not a likely
failure.

Hadn't thought of that. I doubt that there's any reasonable way to test
them.

Thanks,
Bob