Not being familiar with the game, I don't know what "scores Slick" means. Can you help us help you?

I would remove the playfield and give it a good shaking, and remove the mechanical board and do the same until the piece is found.

This is a fun circuit to look at. I'd look at the fact that your lower targets that score "SLICK" or "CHICK" aren't working correctly. Here's the circuit in red that fires the A relay (spots "SLICK"):

SC A relay (resized).JPG

You can see that both the right target switch and the right rollover should both fire the A relay. I'd check that target switch and it's related wiring since you said it works correctly for the rollover switch.

**********************************

Similarly, this is the circuit the fires the D relay (spots "CHICK"):

SC D relay (resized).JPG

If you follow the red circuit, this is how the left target should fire the D relay. Again, since the left top rollover switch seems to be working, I'd just look at that lower left target switch and its wiring.

**********************************

The center target that spots either "SLICK", "CHICK" or both uses the E level switches on your score motor. There are 3 E switches - I've colored them red, green and blue here:

SC B relay (resized).JPG

One and only one of those 3 switches should be closed at each of the 3 home positions of the score motor. The way the schematic is drawn, the blue Motor 1E switch is closed, which means when the center target switch is closed, the A relay fires and you would spot "SLICK".

The score motor turns and that opens the Motor 1E switch and closes the green Motor 4E switch. That means when the center target is hit, the D relay fires, spotting "CHICK".

Again, the score motor turns, and this time, the Motor 4E switch opens and the red Motor 3E switch closes. That means that when the center target is hit, the B relay fires through the red highlighted circuit, which spots both "SLICK" and "CHICK". If that circuit isn't working correctly, I'd check those E level switches...they're at the top level of your score motor. You can see them easily and see if a different one closes each time the score motor turns.

I'd check the switches on the B relay as well, since those are necessary to get both the A and D relay to fire to score both "SLICK" and "CHICK".

BUT, since you say this only started happening when the flipper spring disappeared in there, it's probably shorting the circuit somewhere, causing your A relay to fire more often than it should. As pinballdaveh says, you need to see if you can find it and get it out of there.

That Wayne Neyens was a clever guy!

I just spent a few hours with my Slick Chick. The #2 rollover was not working, it didn't follow #1 like it is supposed to do. Unlatching the wingnuts on the relay rack and turning it up to look and the #2 relay worked fine. Turning it back and retightening the wing nuts and it refused to work, finally tightened the right side wingnut and leaving the back one not tight the relay worked perfectly. It also reset every time instead of sometimes needing two attempts to reset.
Slick Chick also has a lot of pretty sophisticated circuits for an EM. It is a heavy game. There is an adjustment point on the front/bottom of the plavfield that makes the five rollovers turn to 10 points early or late. I'd make sure you have it on "Liberal" as this game is not a simple game to beat. Sam Harvey called it a "Jackpot" game and it is. The rollovers are there to change your mind about your goal in the game. If you can get all four out in an early ball, you can absolutely kill that game. This was supposed to be Dave Gottlieb's favorite game. Wayne Neyens told the story of how it was named. They were having a tough time finding a name for it and they went out for dinner and a few drinks and the sign out front said "Slick Chick" the rest is history Roy's artwork was not cartoonish on this one.

There is a switch on Z (30 PT RELAY) that makes the score motor run. But it acts like one of the 30 pt rollover switches is stuck on or shorted. I'd probably examine the tabs and soldering on the back of each of those switches, examine the switches on the Z relay carefully.

There's also the lock-in circuit for the Z relay. Check that highlighted Motor 2B m/b switch and see if it's opening.

If everything looks good, I might desolder one rollover switch leg at a time and see if the errant behavior stops.

SC Z relay (resized).JPG