Q: About 5BNC vs. VGA
Don't give up on the monitor until you have taken it to a competent TV repair shop that knows monitors as well. For $30 to $50 they can sharpen and focus the monitor to the limit of its tube condition, and estimate any repairs and lifespan remaining. Granted, a tube will fade irrevocably after a number of years but I have taken many un-viewable monitors for the tune-up with an 80% success rate. Much cheaper than replacing and if it keeps it out of the landfill, so much the better.
(Note: Don't take the hood off a monitor and start poking around inside unless you are conversant with high voltage safety precautions or have a paid up life insurance policy. Those puppies have enough juice to stun a horse in them even when unplugged.)