Director 21 resto begins....

[old_tv_nut]

Well, now I'm just fishing, but have you checked component values in the horizontal oscillator/control section? Even if it's getting an input jolt it shouldn't get, I think it maybe should respond with a more damped response instead of a decaying oscillation.
The following three components are the main control loop filter:
C160 .01
R165 3900
C159 0.47

+ other R's and C's in the vicinity

[miniman82]

All the caps and resistors in the horizontal section are either new or within tolerence. I thought I was having a problem with the originals before, but it ended up being a power supply wiring glitch that was my fault. The power supply is fine now, and I strongly doubt issues with the oscilator.