Link John says above "Down on the bottom board there are 2 large square units in the center. These units have 2 coils, one coil steps the unit, the other resets it. When you manually push the lever that connects to one coil, you should see the unit move one step each push through 4 positions. When you push the lever on the other coil the unit should freely slide back to the first position. Your machine is not doing that."
So pop the ball out, lift the playfield and check those two units. Don't try and turn them. by hand work the solenoids in the same way the machine would when the coil fires. One of them will step up three times when you work one coil and then reset back when you work the other. you most likely will see that it steps up the three ok but when you work the other it barely moves in the other direction. Give it a little nudge and it goes back to the proper rest position. Cleaning the contacts/rivets on the rivets side of the disk is sometimes enough to get it to reset better. The better way is to strip it down, clean it up and put it back together. Most likely what was used to lubricate it years ago is now acting more like glue today.
The best thing to do with it is to pack it up in the back of the car and drop it off in Barrie so I can go through the whole machine, I'm not that expensive...
I normally don't make such blatant pitches for repair work - but I sold my Capt. just a week or so ago and didn't get to play it that one last time