my shift cable keeps coming off how do i fix it on my 1996 lumina?

U might have lost a Pin or Clip go ck out a owners repair book or visit a dealer they have the best books at parts dept or give them a call...

Is it easy to access? If so I'd drive up to the nearest pick and pull junkyard and look for pretty much any 1990's GM front wheel drive car and look for the difference. I would have to assume mint is correct and you will probably end up going to the junkyard to get the part anyhow. Unless its a common e or c clip, its very slim finding whatever is missing anywhere else.