What model is your Suntour derail? I would first try to spray the pivot joints with WD40 and see if that frees it up, then follow up about a week later with Finish Line Teflon Dry Plus or Triflow.

The derail may be 22 years old but that doesn't necessarily mean it's time for the bone yard. I have a 22 year old Suntour Superbe (on a Trek 660) derails on my ride and they still work fine with over 145,000 miles.