Welcome to Barco's infamous (very common) horiz. linearity problem Kenny!
It's a common problem - green's horiz linearity is ok from from left right, while red the red grids go wide to narrow, and the blue grids go in the opposite direction (narrow to wide).
... and there's only one global horiz. linearity menu control and pot. @#$&@%! They really should have made 3 separate linearity controls.
There's a few ways to help a bit:
With zone convergence zero'ed play with the the blue horiz width a bit making sure that the overshoot on one side equals the undershoot on the other (you probably already knew this as it's fairly obvious)
Use zone convergence a bit more then usual on the grids 1 and 2 zones to the left and right of the center zone (which incidently controls static conv) because changes to the zones around the center have a huge effect to the outermost zones. Example: Small horiz changes in the zone exactly to the left of center will have a huge effect on the horiz in the zone all the way on the left edge. One click on the zone close to center probably equal 5-6 clicks on the outside zone.
This is useful because one click in the close to center zones may cause very minor (if any) visible changes to the zone itself, while the outermost zone's horiz convergence value may go from very extreme numbers to something more acceptable.
There's two ways to play with the width: The best is to put the elec control to 50 and then use the horiz width coils to get the size right - just make sure when you do this to use a PLASTIC (not metal) screwdriver and make sure AT LEAST ONE of the coils is screwed all the way in. Be careful as the coils are fragile!
Even after doing all this, my left most blue zone's horiz convergence value is at 5/100. They say you should really aim for staying between 30-70 for all zone convergence values. Oh well! It's been stable like this for 2 years now.
The other option is that maybe your 1209's broken... in which case I'd be very happy to take it off yours hands!
(I'd love to get my hands a one of those units - if you ever decide to sell it, lemme know!)