If you are referring to the player select unit on a multiplayer machine those can be twitchy. I messed with one and caused more problems. I use LPS1 which is a light aircraft spray lube a little like WD40. Spray the wiper pins and gently work them in and out to clean them. Spray the fixed contact disc rivets and rotate the wiper disc to clean the contacts. You can actually over-rotate the disc by operating the step lever by hand additional steps then trip the reset lever. Make sure the rest of the mechanism is free. Have some paper towels to catch the drips. Just did this to a Big Chief.

I had that problem with Big Chief. It turned out it wasn’t the player select unit. There were problems with the second thru 4th coin relays (these enable the additional players) or the motorized cam switch. Do you have a schematic? If the machine works ok on 1 player, the problem could be in that area. It took me some time to work thru the problem. It sounds like your player unit is indexing. If your machine is similar, the player unit contacts are in series with contacts in the coin relays. I have a wood rail that uses a step unit to setup the number of players instead of coin relays.