Update
Updating database... Please wait.
Monday 23 April 2018 at 07:34
Just because they are not gummed up does not mean they are making good contact. Those contact points look really dirty. I would dis asemble one more time and clean all contact points and rivits and wiper blade contacts.
Source: http://pinside.com/pinball/forum/topic/williams-space-mission-always-4-players-wont-advance-ball#post-4355687