Rejuving is a last effort kind of deal.
Rewrite sent a good link, its a great starting place. Theres a few really good videos on YouTube as well.
I have bought a number of cabinets that came in from the wild in the US and I am always kind of dumb founded sometimes why the colors and brightness are really wonky. A few simple adjustment usually fixes this for me.
In my experiences though it can be a number of things and it will depend how you want to start and what needs to be done.
Always start with the easy stuff when doing any adjustments on monitors.
Here's some thoughts from my own experiences and readings.
-Read the wiki link above and other information about color adjustments online and on YouTube to get more familiar with the process.
Consider the following 2 items first
-cap change (if you intend to keep this chassis its probably not a bad idea to do it)
-adjust the color gains or bias using the trim pots on the neck board or chassis sometimes they can be on the remote board too. See if it makes any discernible differences.
Failing components can sometimes be as follows:
-corrosion on the color adjustment pot
-broken color adjustment pot or bad solder joints
-bad solder joints on the color transistors on the neck board
-worn out color transistor on the neck board (there are 3, each is responsible for one color)
-worn out tube or color guns
-color gun has lots of deposits inside the neck reducing its output efficiency.
( This is where a rejuvenation can sometimes help. It applies excess power to the color gun and blasts/burns the deposits off the gun. The only side effect of this is it can blast those deposits over to another color gun or put undue stress on the gun. In severe cases it could potentially kill the gun ruining the entire gun assembly inside the crt neck.) In my book this is a final attempt to correct the issue.
Always start with the simple stuff and move your way up only when your sure you need to.