Vintage Synth Repair

Hi!

There is an interesting site (in german): 
http://www.blue-jet.de/index.htm

This guy has some description on the restauration of an OBXa.

Your problem can be caused by the key bushings. The OBXa normally has a 
Pratt-Read Keyboard. The bushings below the keys become hard or even 
fall apart as time goes by... 
Then there can be level problems with the keys.

Check the bushings on your uneven keys. This can be the problem maybe.

Regards,

Ambrosia