you have to be VERY careful with CRT yokes for color CRTs. any slight mis-alignment or slippage of the yoke will throw off the purity and the convergence.

I doubt the yoke slipped, because if it did youll notice a change in purity, and at the very least convergence.

I think a cap failed in the pincussion or keystone correction circuit, you just corrected for the symptom, and not the cause. The one thing that is sticking out at me for this reasoning of thought is the fact that the bottom is at a slant much larger than the top. usually the slant will be equal if the yoke slips.