When my 1991 245 SE is hot, the starter won't crank until it cools down or I jump it off. I have had success in a pinch to pour or spray water over the starter. To me this seems like a starter or solenoid issue and that I should replace my starter. Could it Be anything else?
John B.

"jump it off" What does that mean?
As a diagnosis try applyiing 12V with a small jumper wire from battery plus directly to the small wire on the solonoid? Also check for presence of 12V at the large starter terminal. This will tell you for sure if it is the starter or not.
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David Hunter

Check the basics--connections at hot wires and especially the grounds. Other than those items it's most likely to be the starter. -- Dave