Yes if wiggling the cable around fixed it then the cable itself is pretty much on the way out. you can wiggle them for months to keep them working but it will eventually stay purple.
The good news:
They tend to look like they can't be replaced but they can.
Those cables have a connector inside the CRT that unplugs and you can get it replaced. This does involve taking the cover off the CRT.
The Bad news :
I do Not recommend you do this unless you know what the heck your doing. CRT's like regular old tubed TV's Store Very large charges of electricity inside the tube ( 20,000 + volts ) and reaching around inside them can discharge them right into you. which at the very least will hurt like hell and can cause 3rd degree burns in a small area. And it can kill if the jolt hits you wrong. like traveling through the heart =>. Aren't I just a wet blanket?
Leaving the monitor off for a few days or so and unplugged generally discharges the tube on its own.
If you really like the monitor and don't know what to do or what not to touch, pay a professional to change the cable over. It will probably cost about 60 bucks. Lots of those cables are interchangeable, but not all. Computer recyclers tend to save a few of various types just for that situation and the monitor repair guys" which are getting harder to find around here" also tend to have a few.