Summarizing, it seems the problem of uneven velocity response in our case was caused by:
Dirt on the electrical circuit in the keyboard bed.
Not under the rubber switches themselves, but around the soldering contacts on the circuit.
Hi, sorry for digging this old post out!
I am having the exact same problem with different keys. I just tried to clean the keyboard inside, but it had no effect, but I might not have gone far enough with the cleaning:
Are you talking about the long boards which are screwed on the back of the keys, the ones which contain a series of resistors (or were it diodes, I didn't check^^)?
Did you actually screw them off the keys, so you could reach the soldering contacts on the other side?
Cheers for help!
Gernot