boxburn

The starter motor may be finally dead. When mine died it wouldn't start, then would a few times then just wouldn't again.

The ignition switch can cause faults on these too.

If you got a multimeter out and checked for voltage at the trigger wire on the starter against a good ground while someone tries to turn it over (in Park or Neutral parking brake on), it may help narrow down the fault. If you read a good 12v it'll be the starter, if it's a low voltage, try again with one lead on the trigger and the other on the starter's battery feed. If it reads a low voltage, I'd guess starter, if it reads a high voltage then I'd say connections/ignition switch. Cruiser54 has a good picture of what happens to the connector for the ignition switch somewhere.

Roler

Boxburn's steps are a good way to discriminate/isolate the starter.
A quick and easy way to define if the NSS is (still) a possibility is either bypass it with a small jumper wire in the connector or remove the starter relay and jump terminal 30 and 87 with key on. I'm positive this and Boxburn's instructions will give you the answer.

Edit: Just thinking about your slow crank; I'd have the battery load tested as well, to make sure that besides holding the voltage after your charge, is also capable of delivering the amps needed to start.

Seabee

I recently purchased one of the $48.00 Amazon units and it seems to be a quality part. Works a treat!

Dibbons

Update: I replaced the starter/solenoid with a rebuilt unit from Autozone and solved the dead start problem (the part number in Mexico is DL17006). The motor now spins very quickly (no comparison to how it was barely cranking over the last few weeks). I guess it did not hurt to clean up the NSS switch, but that was not the heart of the problem. Thank you everyone for your above input.