Red Flickers

[lnx64]

I'm thinking either the CRT is getting a short, or the red bias POT is flakey.

I haven't adjusted it or taken it apart at all lately cause it's been working so well, but lately the red colors flickers a little, gets bright, normal, bright, normal, and it messes with the grayscale tracking too..

Where should I start? It seems completely intermittent, but only seems to do it once it's warmed up.