Vintage Synth Repair

Hi Folks,

I'm in the process of restoring my Optigan, and I have a question about
the drive mechanism.  On mine, the brass flywheel that the rubber drive 
wheel rides against has a coating of rubber and I'm not certain whether 
this is by design, or it's residue from the drive wheel that needs to be 
removed.  If it isn't supposed to be there, this could be contributing 
to my speed/pitch problems.

Does anyone have one of these that they could take a look at, for the 
sake of comparison?  Or, if you are familiar with how it is supposed to 
be, so much the better.  Any assistance would be appreciated.

Thanks,

George