B48 starting problems

I didn't install improvement kit. I got this 420 with over 1k hours.
I haven't replace the solenoid.
Battery is <6 mos old, has clean terminals and clean ground.
How do I check the solenoid?

Chuck,
Starter did not engage during the jump. Got some sparks.
Battery shows 12.7amps.
Suggestions?

knotty, flywheel is free.

I will jump it tonight.

Chuck, I had a trickle charge on the battery through the night. It now shows 13.7 volts. Still no starter action when jumping the solenoid.
I also tried to jump it to the battery with cables from my car. Still just get the one click.
Starter? The battery is < 6mos old. If I trickle charge it over night, will that confirm its a problem with the starter?
The volts drop to about 12.5v when I jump the solenoid. Should I put my car battery in to just be sure?

Couldn't resist. I put my car battery in the 420. Same result. Should I pull the starter? What type of shop do I bring the starter to?

Is it as simple as replacing the brushes and springs or is it more involved. I see rebuild kits available on the interweb.

Can you point me toward starter removal instructions?
There are some new starters on line for approx $100. Should I stay away?