Old, 1991 Magnavox TV (RR1938 W121) Video Problem

My old 1991 Magnavox TV (Model # RR1938 W121) suddenly went from a perfect picture to a picture that looks like it has a bright greenish-yellow filter or "fog" on top of it. There are also bright yellow retrace lines on top of the picture. The audio is still perfect. The only colors that seem to make their way through the "fog" are flesh-tones, orange, white, and cyan. When this first began, a week ago, the picture would start out somewhat viewable/recognizable when I first turned it on, and then fade to a solid greenish/yellow with retrace lines after an hour or so of operation. Now, when I turn it on, the picture only remains viewable/recognizable for about 3 seconds before fading to solid greenish-yellow with bright yellow retrace lines. I took the back off the TV and very carefully vacuumed out 21 years of dust, but it did no good. Any suggestions for a fix to save my old antique? Thanx.