Tonmaster advice (in English if possible )

Hello all, and all the best for 2016...

I have the most puzzling problem with my Tonmaster, and I would welcome any advice, including comments about possible causes, and even comments about things to eliminate as not being possible causes of the problem.

I have a fully rebuilt mech, and the record stack turns smoothly and freely with a gentle twist.
I have tried two different GeFaG motors, both in good condition.
I have tested (in our electronics lab) to a limited degree, the start capacitor.

So what is the problem?

After selecting between one and three records, the records begin to run more and more slowly, and the motors (either one) become warmer than I would be happy with!

The two idler wheels turn freely. Everything turns freely!

I dont see how a failed start capacitor could be the cause, but I am no electonics engineer.

Any suggestions of further things to check?

Best regards

Morgan in Luxembourg