[Mr. Lim]

Originally Posted by Ether

I hope you're right. Better that than an engine computer problem.

I'll give it a try tomorrow afternoon after the kickoff.

But in the meantime, can you think of (an even remotely plausible) reason why this happens only under the conditions described in the OP ? That's the part that's stumping me. I've repeated this about half a dozen times over the course of the past week and it always follows the described pattern.

When the starter heats up and cools down, parts of it expand and contract. With worn brushes/armature/contacts/carbon deposits, that expanding and contracting could be creating just enough clearance between contacts such that your armature loses electrical contact. Letting it cool allows things to contract, and the clearance disappears. That's why whacking it with a hammer is an effective test.