Vintage Synth Repair

I recently bought a Wurlitzer organ model 4075.  It's from the 1970's I think.  Anyway, it is in pretty good condition except some of the keys don't work.  Can anyone help me by telling me how I might be able to fix it?  Is it very difficult to clean the contacts?  How can I access the upper manual?  Any help would be greatly appreciated.  Thank you.
Rick
rtgreen2@...