OBERHEIM SYNTH

I have a question for anyone that has used the X-Mod on an OB-X.  When
I use X-mod (aka cross modulations, aka linear FM), each of my 7
voices produces a different pitch, some more different than others. 
Now my board is in pretty darn good (but not perfect)
tune/calibration.  Because of this pitch problem, when I use X-mod
have use unison and X-mod has been delegated, for the most part, to
making strange noises.

Now my question: Is this the best I can hope for or is there a way to
solve this pitch problem?

My guess is that this is the nature of X-mod and unless a board is in
perfect, perfect calibration, this pitch problem should be expected. 
(And given the age and design of an OB-X, perfect, perfect calibration
is impossible.)  It is also my guess that this pitch reality is one
reason why X-mod did not make it to the OB-Xa and the OB8.

Any thoughts out there?