Still having a problem with the RED color fading in and out...

I'm not sure where to start troubleshooting for this problem. The picture is great when the red is working. Then it just slowly fades out until there is no red at all. Sometimes it will eventually come back, other times it takes messing with the red, green, blue and bias pots on the back. The crt hasn't been tested. Should this be my next step? I'm not sure what the signs of a weak red gun are? Seems to me that if there was a problem with the red gun, that it would always be bad.... not fade in and out. Maybe something in the color demodulator section?