DEC VR01-A Display Unit (AKA Tek RM503 oscilloscope)

I just got ahold of a Tek RM503 oscilloscope. According to some documents I have found DEC sold this as the VR01-A. This one is probably not from DEC. First, does anyone know if there were any modifications made to use it as a point plot scope? It looks like there was just a cable that connected to the Z-axis/crt grid input on the back. Second, this scope has differential amplifiers for both horizontal and vertical inputs. I can't get the amplifiers to balance and so for any setting more sensitive than .1v/cm I can't get the trace on the screen. This shouldn't be a problem for how I want to use the scope, but I would like to have it fully functional and calibrated. Digging around inside, I see that the bias voltages for the cathode followers are not the same and this throws the whole differential amp out of balance. It can be compensated for at low gains by using the POSITION knob. If there are any valve or Tek scope experts out there, they can contact me offline so I can ask some naive questions about tubes. -chuck