60's RCA radio muddy audio

[TUD1]

Got this beauty at the radio club this morning for $10. I cleaned the controls real good, but it's still having an annoying problem. It sounds excellent most of the time, but every once in a while, out of the blue, the audio will get very muddy and distorted. Most times it will fix itself after a while. Tuning doesn't help, and it's on both AM and FM when it messes up. Any ideas? Somebody at the club said it's either the discriminator or the IF needs an alignment. I think it's just the big blue filter caps.