Agree with all the above. Also check all caps and resistors in the color sync circuit while you are at it, and clean the tube socket contacts.
I agree the short answer is most likely the crystal.
In answer to your other question, I don't think any color sets of the old variety ever used a crystal with a frequency of anything other than 3.58 Mhz. Especially not Magnavox, RCA, Zenith, Sylvania, GE, Curtis Mathes... you get my point.
