IBM 5120 monitor issues

Well, here I am again soliciting advice from you guys. One of these days I'll be able to answer someone else's question and I'll feel useful :). Anyway. I picked up an IBM 5120 (i.e. the "really big and heavy" (with emphasis on "heavy") variant of the 5100/5110) awhile back that has a few issues and I've just now got enough spare time to take a look at it. Finally got done cleaning out copious amounts of gooey black tar that used to be foam 25 years ago... There are two major issues, the first being the monitor, the second being a ROS error on startup (which I suspect may be quite difficult to solve...) But I'd like to see what I can do about the monitor. The picture exhibits a strange behavior that I can't say I've seen before. The horizontal retrace seems to "fold" over itself in the middle (like the electron gun is doing a "loop" in the center of the screen for each line). I've taken a (terrible) picture of the fault and put it at: http://yahozna.dyndns.org/scratch/5120disp.jpg). The picture's also a bit jumpy. I've tinkered a bit with the various adjustments on the CRT's PCB but it doesn't make any appreciable difference. The monitor is labeled as a "Ball TV 90." I've done a bit of maintenance on old Arcade monitors, mostly of the "cap kit" variety so I know how to be careful around the HV sections, but I'm not much for troubleshooting (yet). Any suggestions on where to start? While I'm at it -- anyone have an archive of software for this thing anywhere? I haven't found much, I'm looking for floppy images (the 5120 has 2 8" drives). Thanks again for the advice... - Josh