Trimmer Cap Question

[Chris K]

Hi all. Trying to track down a “twitchy” horizontal frequency signal. The trace isn’t stable and jumps every second or so in frequency going way out of range and then stabilizing. It’s the correct shape…just twitchy. There are mica compression trimmers for horizontal drive and lock in the circuit. I’m wondering if they might be the culprit? This may be a stupid question but do these trimmers get silver mica disease? Can they intermittently short?