67 barracuda speedo issues

Bouncing needle is often caused by a bad cable. Checking for a bad cable by holding one end of the cable in a vice and while holding the opposite end try to twist the cable in either direction. If you can twist the cable in either direction 1/4 turn or more- you have a bad cable, make a new one. The proper lubricant is a lite grease. If the cable is known to be good, then your speedo head needs servicing.