Refer to ASM handbook volume 18: Friction, lubrication and wear technology (Oct 1992).
Please mention the type of material the metal stopper is made of. Cold welding happens when there is mutual solid solubility between the interacting materials. Let us consider a simple example. Copper and nickel have 100% mutual solublity in solid state whereas lead and copper have very limited solubility. Therefore, copper and lead are less likely to cold weld in comparison to copper and nickel.
Possible solutions include:
1. Lubricate if your system design allows either with a solid or liquid lubricant
2. Change the interactiong pair (from gold to X-metal stopper to something that with poor or no mutual solid solubility). Here I assume the interation is between gold and the metal stopper but remember the gold plate might have worn away, resulting in a situation where the substrate metal is interacting tribologically with the metal stopper.
3. Have suitable coating on the metal stopper.
Best wishes
CDotS