OHBowler,
I have rebuilt many Rudell style jigs such as yours. It sounds as though the clamp (sometimes referred to as a Sta-co clamp) is worn out.
Innovative Bowling (tell John Jamieson that I sent you) or Jaywawk Bowling Supply carries new clamps, stoppers, etc. If you're going to replace one, then you might as well do both sides.
I hope that this helps!
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Gary Palma
X-act Reaction pro shop at Ideal Lanes
119 Jennings Street
Endicott, NY 13760
(607) 760-3700