HH Scott 222C Amplifier 7189 tube red plating

I’m considering restoring an old HH Scott 222c amplifier that I have had since I was a teen. It has not been powered on in about 20 years. I powered it on today (nothing blew up thankfully) and noticed that one of the 7189 tubes was red plating. I quickly turned it off.

I then swapped the tube with another 7189 in the amp and the red plate followed the tube. I believe that this would mean that the tube is bad. Does anyone know if I am correct in this diagnosis?