I've restored a B2, which is smaller but exactly the same mechanism. Photos here:
Multico B2 TLC
In short, the parallelogram set up *should* mean the table rises and falls exactly equally and there isn't an adjustable part to resolve it.
If the parallelogram isn't parallel, then one of four things is happening (all bad I'm afraid):
1. One or more of the H "hinge" pieces is worn. This could make one end rise/fall more than the other. It would also mean that the deflection might change over the rise/fall. You'd need to somehow fill and rebore very precisely.
2. One or more of the spindles that run through the hinges is worn or bent. Impact as above, but easier to replace with a silver steel rod.
3. The mounting holes in the tables or body are worn or damaged - see #1
4. The mounting holes in the main body are worn or mis-positioned. This might mean the error was constant on fall/rise.
I would do some experiments to see if each table goes up and down parallel to itself (if you see what I mean) - my guess is outfeed will be fine as it gets moved much less and so wears less. After that, you've probably got to take it apart and look for wear.