OP here. I do not believe that it is a bad solenoid. The starter engaged as soon as I jumpered the solenoid from the 12v lead. Cranked good. This happened once about 10 years ago and never since. Maybe I will be good for another 10 years. LOL
I replaced the factory seat with a suspension seat years ago and jumpered the 2 seat safety switches as it was not compatible. I will start looking there first.
Are starter solenoids as easy to repair as they used to be 20+ years ago? Then it was just a matter of removing a few screws and filing the contacts.
Starters themselves not much harder to do. Both on the same order of difficulty as an oil/filter change.
It is sometimes more cost effective to replace the entire starter than just the solenoid. And in instances where it is not necessarily the most cost effective option, there is a school of thought that is not in favor of putting a new solenoid on an old starter at the risk of a near term starter motor failure. It all depends on the relative cost and availablity of each and the mindset of the person writing the checks.
Normally on something simple like a starter/solenoid I just unbolt it, take it apart, repair as needed, and put it back on. There's nothing complicated here, and it is certainly true that both starter and solenoid tend to build up corrosion and dust inside.
Before replacing anything, do comprehensive checks with a voltmeter to determine where the voltage drop is occuring. Us the scientific method, develop a hypothesis, then test that hypothesis.
Remember this, If your tractor won't start, the very LAST thing the problem is likely to be is the starter. Or for that matter even the starter solenoid. There are MANY other reasons for a no start (actually a no crank) situation than a starter. The starter is the LAST place to look from a probability standpoint. Cabling and connections are the FIRST place to look. Even before battery failure. Although it only takes a few seconds with a voltmeter and an assistant to rule out or in the battery as the failure point.