A crt can't quite develop a bad pixel in the same way an LCD can. The closest failure mode is screen burn, where a stationary pattern is displayed for so long that the phosphors actually cook a bit, causing a permanent ghost image of that pattern. But I'm sure you already knew that. And that screensavers were invented to prevent this problem.

As for focus drift, many things can cause it. Excessive brightness is a common culprit, so if you're someone who likes to crank up the brightness to the max, back off a bit and see if that helps.

If that isn't the problem, then post back.