There are no deflection coils used with oscilloscopes, just deflection plates inside the CRT.
Right, my 50-year-old scope has plates, not coils. But I couldn't be sure about every other scope. I've seen coils in tv's.
thanks for your comment. do you mean there's something physically wrong with the coil or it's an electrical problem?
A tilted coil would be one way to explain a physical cause for the problem if we were talking about a tv rather than an oscilloscope.
Instead we will assume your scope has deflection plates. It is not likely for a plate to get tilted, misaligned, etc.
The problem is that your horizontal scan has changing amplitude. The further the beam appears down the screen, the wider the horizontal scan gets.
If it were a computer CRT monitor we would say the image has a trapezoidal shape. This shape can be adjusted by calling up the various settings (in monitors made in the past 15 years or so).
Does your scope have such a choice of settings?
Or maybe something has happened where the horizontal scan circuit is now affected by the vertical deflection circuit. To troubleshoot this would require you open the scope and try some meter readings. You would need to find the test points for the circuitry driving the horizontal scan. Readings would be a couple hundred volts.
The horizontal scan width has an adjustment. Probably a potentiometer. If this developed a bad contact (perhaps the ground) then the horizontal scan might be influenced by other circuitry.