Cub Cadet 1320 Hydro. About 20 years old now and still going strong. This is the second time I've replaced the starter solenoid. under the seat, next to the battery.
When the battery is weak, the solenoid makes a very rapid clacking noise and the starter does not turn. This last time with a fully charged 1 year old battery. I put in a new solenoid and decided to open up the old one to see what's going on.
Drilled out the 4 rivets and pulled it part. The main contact is a disc on a spring loaded plastic pin that gets pushed by the coil plunger. You can see the contacts are pitted but are relatively carbon free.
I suppose I could bolt it back together but new ones are $9 and work better.