[DaveWM]

B&W has magnets in the yoke, color uses active circuits. Assuming its a BW set I would look for magnets in the yoke that may have fallen out or become weak.

It does not look that bad, back in the day you did not have black bars on top and bottom for wide screen format to show minor defects like this. (I was looking for classic pin cushion defect this is opposite of what you would expect, like too much pincushion correction).

after looking again I think I see what the prob is the bottom looks a tad pulled in on the right. If it was a color set I would look to see if there is a connection from the screen of the horz out to the vert, this was how some zeniths corrected pin cushion but again only on a color set. the pic is in BW so I assume its BW, pin cushion effect should be the opposite.

check B+ and try new horz sweep tubes.