[Capt Len]

If the starter motor brushes and commutator are not healthy that's what you can get. A little bilge oil and water ?? If starter wherrzz but doesn't engage look to the Bendix spring and or shaft it slids on (ford type)

 

[Capt Len]

Take an old solinoid apart to see that the two bolt ends that are the terminals are corroded. More important is the copper end of the moving part. When it pits up too bad it may or may not connect across the bolt ends and can be temp sensitive. (Click,click) If you turn it 90 degrees you can get some more life out of it .That's pretty haywire. but I've done it in the snow up a logging road.