Anyone have experience with a D20F1U? Geometry question

[Grahambelmont]

I recently got my hands on a d20 and I love it. Amd everything about it is nearly perfect, however it has one issue that my brain refuses to ignore - there's a very slight horizontal linearity problem. The far right side is ever so slightly wider than the rest of the monitor. Luckily its a minor difference but it still produces a noticeable warping effect when scrolling.

I've found the E board menu and the linearity controls within but even at their extreme values there's very little effect. Looking through the manual I noticed there were horizontal linearity circuits listed on the E board. Does anyone know if these are the set or adjustable variety? I'm a little intimidated to open the thing up so I didn't want to go through with it just to find they can't be adjusted either way. And if not, is there anything else I could look into that might resolve the issue?