Isn't there a selector switch underneath the 5000 for the cartridge type Craig? I'm not convinced this would cause your problems though as I don't know what effect this has on playback if it set incorrectly.
Underneath the tonearm pivot assembly there is an antiskating device on a fine spring connected to an adjustment lever (I think) - maybe this has become detached and causing the needle to jump - but I'm clutching at straws a little to be honest, it's been quite a while since I had one of these beogram types in bits....
Chris.
The use of metaphors should be avoided like the plague. They're like a red rag to a bull to me.