OK, make all the jokes that you know you want to do !!:D

The set in question:
Magnavox model RD4258SL
serial 34366294
dated July 1984

The problem has gotten more noticeable in the last few weeks. If the scene on the screen changes or the program goes to a commercial, the tube will flash to white and back to image rapidly. If I change the brightness control to darken the image then the screen is almost too dark. The problem also occurs when I use either a VCR or DVD player.
I am the second owner of this set, bought from the guy that got it new in 1984. He also gave me the remote and owner's manual. I've had it now for about 3 years and this is the first problem that I have had with it.

I've been digging around antique tube radio sets for the last 6-8 years now. Put together a component stereo system in the last year. Found this site and use it for reference. But up till now have never been into a TV set. So whatever help offered will be appreciated. I do have friends with a considerable amount more knowledge and experience in electronics and I know that they would help me out but I could use a starting point before I dive into this.

Thanks for any help

Magnavox? Were I to guess, some capacitors are drying out in that TV.

Yep, I would bet on caps first. The symptoms make me think of a HV regulation issue, but I don't know much about solid state stuff. That might be a good place to start, anyway. I had one set with squirrely regulation (older than this, but solid state) and a book I have said it could be leaky diodes in the circuit.

If I change the brightness control to darken the image then the screen is almost too dark.

This makes me think of the brightness limiter circuit. I had an issue like it with a 1985 GE Performance Television. It would flash to bright like you said, and go way too dark if you tried to do anything. it did it really bad until it went though the warm up cycle. Is yours worse when the sets cold? Just a thought.........