Hi,

I never succeeded in cleaning the original bend pots.  It might help a
little, but surely doesn't solve your dead band problem.
As posted  by others, a stable dead band is VERY essential for a correct
OB-Xa tuning.
If you don't want to replace the pot with a new one (special type), try to
include the diodes which IMHO is easier to do than the pot replacement,
provided you are handy with the solder gun (grab it on the right end...)

Good Luck

Mondo