If I was asked to guess - my WAG is a pilot bearing going bad. That's the bearing in the center of the flywheel that the nose of the transmission input shaft goes into. Usually it just spins. If it starts to drag probably the only symptom would be what you've experienced. And perhaps some noise under the conditions you're seeing the tire slowly spinning.I had an incident this morning that made me think of this thread. I am in the process of doing a brake job (pads & rotors followed by flush) on my 2010 Cayman 2.9L MT. The car is up on Quick Jack with wheels off. I just finished the last (left rear) wheel and wanted to test that the new wear sensors were all working, so I started the car and stepped out. It was in neutral. I noticed the left rear rear hub/rotor as slowly spinning. That's what reminded me of this thread. The right rear was stationary. After double checking it was in neutral, I put a gloved hand on the rotor and easily stopped it. When I let go, it remain stationary, but with a slight nudge, it started again. Is this normal?
Oh, one other odd thing associated with the above. I was able to start the engine without getting in and pressing the clutch or brake. I assumed my clutch switch is faulty and don't think it is related to the rotation.
Manual Transmission Pilot Bearing Diagnosis
Pilot bearings make their most noise when the pedal is completely depressed. The pilot bearing makes noise when the input and crankshaft are rotating at different speeds. This works the bearing. Diagnose the pilot bearing in comparison to the release bearing.
5 Bad Pilot Bearing Symptoms (and How to Fix It) - My Car Makes Noise
The clutch and transmission have two crucial bearing types; the clutch release bearing and the pilot bearings.