Slight shadow on my Chromacolor II picture - ideas ?

[Snade]

This is the Zenith Chromacolor II (1975) that I picked up from Doug. I love this TV and use it all the time.

In the area I have circled below, a greenish shadow has developed on the left side of the screen. It's kind of subtle, but noticeable when the TV is showing a white background.

Any ideas?



Thanks. Mark (aka Snade)