Dave,

               Thinking about your starter problem suddenly brought back sad memories from over 20 years ago when I owned 2 Claas 106 headers (ag machines) which were without doubt the greatest Lemons that Claas ever produced , and I had 2 of them. Besides the usual grief these monstrosities  gave, the engines always started and ran beautifully up until about 2000 - 2500 hours.  The engines were V6 mercedes diesels with Bosch starters. Then once these hours were reached they would start cold perfectly, but once hot refused to turn over until cold.  The starters just did not throw in at all.  To remove the starters required the Cab to be tilted forwards which opened up a small gap between the cab and the engine bay. By sliding down like a snake, one could then remove the side  panel of the engine bay --- all at red hot in the middle of summer.  With the engine bay cover removed it exposed the starter for removal.  Only trouble was that the exhaust manifold had to be removed first to get to the starter!!  Trust me it was such a joy that it was sheer desperation to be forced to remove the starter.

Every time the starter would turn over perfectly on the bench. Disassembled and resembled many times for no fault whatever, they always performed perfectly on the bench, but hot in the machine--- no way.  Then about the 10th time and many hours later  on the bench it was getting dark and when the power was applied to the starter, sparks flew from the rear cage of the starter.  In broad daylight it would never have been picked up.  The rear cage held the brushes and was solid riveted  to the main body and had to carry the current between the two parts.  After drilling out the solid rivets it was obvious that black corrosion has set in and effectively insulated the Brushes cage from any current when hot. Without having seen it I would say it was impossible.   All was cleaned up, re -riveted  and soldered for good measure and Whacko, all worked as it should hot or cold.

Does it have any relevance to the rotary starter??? I do not know, but a change of starter would tell all.  The corrosion in the Bosch starter accumulated over 2500 hours and would never had been picked up without that chance test in semi darkness.

Suggest all connections to the starter be meticulously cleaned as the slightest corrosion may stop current flow when hot, or impede enough that it just drags current away for no effect.  A bad connection will heat, drag current away and effectively react as if the battery is half flat.   Also never buy a Claas 106 header unless you wish to learn to swear.

Neil.