RCA Victor 21-T-8205 White line in middle of picture

[ThePlague]

Hello all, thank you for the help providing awhile back on this set! It has had a full recap and is working like a champ. I've been able to run it for 4-5 hours continuously without any issues other than the occasionally user control adjustment. The one thing that is persistent before and after the re-cap is the white line in the middle of the picture. It is more noticeable in images with lots of blacks or darker colors. It moves with the horizontal hold adjustment as well. Is this a fixable issue, or just something to get used to given the age of the set? I'm not certain what it is called specifically, so googling hasn't given much insight. Thanks again!