hi
I recently recieved a (free) pc monitor. Its all scratched up, broken etc. I fixed it for the most part. Because the monitor cord was horribly small, I went to radio shack for an extension cable. I was happy with it, but I noticed a small line straight down the monitor. I decided it was time to use my apple display again. Upon plugging it in, I was horrified with shadows on everything. I realized it was the extension cable.
I would not know what to do in your case, except for experimenting.
Try them with different computers. see if you can get some more free monitors in case something goes wrong. My ideas include altering settings, such as moire, horizontal/vertical convergance, contrast etc., using a degaussing coil instead of trusting the monitor's own chip (tv repairmen have coils, borrow one). if all of these fail (as you have probably tried all of these), then let it sit for 24/48h, and open the case. blow out dust etc., and then look for knobs or dials inside the monitor (maybe on the neck of the crt). there might be glue, but since its old and used, the glue is probably brittle. if you can stand the danger (rubber gloves?), plug it in and carefully fiddle with the nobs. watch the display for changes and if it works be happy. of not it could be the cable. try buying a (good and perfectly working) extension cable, cutting it, and replacing the one inside the monitor.
In other words, those words men find it so hard to say, " I don't know".
If it works, be happy. If not, buy glasses.