Vintage Synth Repair

Hi, 
I bought a Wurlitzer Omni 6000 organ at auction this past weekend.  
Everything seems to work fine but three keys, one on the upper 
keyboard and two on the lower one, require an awful lot of pressure, 
much more than I can muster up playing the instrument.  I almost have 
to "lean" on the key before I hear a sound.

I'm looking for a fix for this problem.  Since I do get a sound when 
I put enough pressure on the key, I think the electric contacts are 
fine and I'm dealing with a mechanical problem.  I opened the back of 
the cabinet but am hesitant to find a way to pull the keyboards out 
and perform "surgery" since I have no experience in the area of organ 
repair.

The instrument is very clean and I doubt that enough dust, or dirt 
has collected under those keys to cause this problem.

Also, since Wurlitzer went out of business some time ago, I wonder 
who to turn to when any more serious problems pop up.

Any input you can give me is appreciated.

Regards,
  Jeff