Speed drops on cassette deck

[Jeffro10]

I have a Marantz SD1000 I recently restored, when playing back a cassette the speed is steady for about 10 seconds before it slowly drops significantly, it has new drive belts and the pinch roller has been restored, would it be a capacitor or any of the kind?

Thanks heaps.

 

[davcon]

Could be the capacitors and or the dc motor.