Ooh. I'm the xm501 master! Meaning that my xm501 kicked me in the teeth for about 6 months so I've had a bad time of it.

The big aluminum can capacitor is suspect. But on that monitor I would expect the hum bars to look a little different. So I suspect Ken is right about the game board. That's Stunt Cycle, right?
Check the following:
1) On the monitor chassis, measure the AC volts for +73 and +30 supplies. These can be most easily found on the pins around the edge of the chassis. You can connect the meter's negative lead to the chassis ground.) The less AC voltage the better.
2) On the game board, check the AC and DC volts going into/out of the LM309 regulator. Easiest way to do that is to clip the negative lead to the minus lead of the 8000uF electrolytic cap. Then check both ends of the big 10W power resistor with the red lead. At one end of the resistor, the DC voltage should be very close to +5V and the AC should be very small (ideally = zero). At the other end, the DC volts should be "higher" than +5V. Hopefully no lower than about 7.5V. The AC measurement will depend on the load.
Your problem is with one of these points. (or maybe a little of each)
Oh, BTW....for me, "monitor" means "tube + chassis". So yeah, I mean the chassis. Sorry.