Quoted from LTG:Screw won't help if it isn't getting stuck.
It sounds like your problem is the mech isn't level. Think about it - Coin mech is at a right angle to the coin door. Playfield is at a 6 1/2 degree pitch. Whole game is at a 6 1/2 degree pitch. So your mech is leaning to the coin return side.
Put your mech on a level surface and see if coin goes to return or the coin switch side. If it works on the level surface, then you need to find different mechs that will work or get your mechs leaning back the other way.
Been a problem with pinball since they started mounting the mechs in this fashion.
Stern is the only one to recently rout out more wood and lean the whole door in a bit.
LTG
I have this same problem on my new Stern Star Trek. With the game set for the proper pitch the coin mech is leaning to the coin return side. The quarter coin mech's that came with the game work fine. The coin door and mech's are Suzo-Happ. I like to use .984 tokens in my games and I have always used the Happ .984/quarter combo coin mech's and they work great in all my other games but they don't work in my new Stern Star Trek LE pinball machine. They work with the door open but when closed they are not level and tokens pass to the coin return. You would think a company like Stern as long as they have been making pinball games would have a clue about how to angel the front panel of the cabinet so the coin mech is level.
For now I put the game on free play but the only .984 token mech I have found so far that works is the black plastic Imonex brand which seems like my only option. It just seems crazy Stern cant get it right after building so many games. It is too much to ask? Apparently so.