pushing the play all button any time the playfield shuffle (bally calls it "shutter") is closed will cause the shuffle to open...that resets the game. The key to figuring out the schematic is when "normally" is.

in this case, the shuffle switches are drawn when the shuffle is closed, so the 2nd position shuffle motor switch that is NC at schem B6.5 will cause coin relay switch 3 power the shuffle motor.

wrt wiring changes for free play, you can rip all that out and put it back to factory if you want. Misadjusting the SPDT replay register zero switch ("R.P. S.U. zero sw") at schem B2 so it always connects wire 65 to 45 is all you need assuming you don't care about the coin meter (if you have one) working right. The game will function normally - resetting credits at power on, etc. - except it will also cycle when the register is 000 and never accept a coin (if your coin lockout coil/armature works).

the replay register always decrements when the game cycles if credits are > 000. When the game left the factory, it would reject an inserted coin if the register was nonzero. Operators often disconnected the coin lockout because it tended to make a buzzing noise, and also if you are daft enough to insert a coin when you have credits, that improves the profit margin

you have the game mode vs. coin mode thing pretty much figured out. The only thing to notice is the Play All pushbutton sw. 1 at schem C2.5. When you push the play all button, that switch opens and removes the power from the extra ball pushbutton relay. When you drop a coin, the game will reset.

the wiring disabling the buttons when the shuffle was closed may have been for someplace like ohio where replays were illegal. They got around it by requiring the game to be reset with a coin. Cycling the machine further using replays must have been legally fuzzy or nobody thought too hard about it.

shorting all play switch 1 I don't see the point of either. Was the game in coin mode?

are the motors in the game the original merckle ones - round gearbox with a couple thumbscrew-looking oil cups for the rotor bearings? if so, a drop of oil in the cups is okay, but probably not needed.

I don't put oil in the gearboxes as it just leaks out. If there's a way to open a merckle gearbox, I dunno what it is. If they had leaking liquid oil in I removed the motor washed it out with solvent thru the screw hole in the side of the gearbox case, then injected some grease. Otherwise I leave them alone.

you can remove the conical nuts holding on the stator and bearing with pliers...but they may be left-hand thread and if they are seized you can bust the bolt section or strip them, so if the motor is working I'd leave it alone.

Butch probably has a better answer for motor lube.

I will eventually grab a Manhattan parts head from the pacific pinball museum and document the mixers and reflex unit. Based on the schem, it's likely they are the same as Pixies except maybe some rivet wiring on mixer 2. You can find that documentation on http://bingo.cdyn.com/machines/united/pixies. If your game is playing reasonably well (i.e. you are losing, but not obscenely quickly), then you don't need that info.

those are merkle-korff gear motors. The name/info is stamped onto the face of the gearbox, so you can't see it until you remove the motor from the mounting bracket.

I removed the outer bearing and stator from a control unit one last week and washed out the gearbox with solvent. I used both spray brake cleaner and denatured alcohol, then squirted magnalube into the gearbox with a syringe. The conical nuts are reverse-threaded, so you twist them clockwise to unscrew. The fan was pressed on and pried off easily with a couple flat bladed screwdrivers. If there's a way to get into the gearbox itself, I don't know how. It looks like the gearbox was soldered closed or the face plate was inserted into a heat expanded case and the case shrunk as it cooled. I don't have a disposable motor to experiment with at the moment, and getting the gearbox apart isn't worth the effort to replace the grease.

what you put back in the gearbox is probably not critical. Liquids will weep out, and originally it was some kind of grease. If you want to use something more liquid to dampen gear noise better, use thick stuff like heavy weight transmission fluid or add in some miracle goo like lucas oil stabilizer to boost the viscosity way up. Keep the liquid below the shaft/rotor holes level to minimize seepage...the rotating gears will pick up the oil and carry it where it's needed.

the main reason I took the motor apart was a lot of dried oil on the rotor causing binding with the stator. The motor was pretty much frozen … hard to spin the fan even when motor removed from control unit shaft.

the mixer shaft has a few more clutches than the control unit, but the effort to spin the fan blade with your finger shouldn't be hugely different. You should be able to spin the fan and slip the clutches without making a deep notch in your skin.

wrt to how scores/features improve, the reflex unit wiper position impacts that a lot. In general, tho, united games seem a bit looser than bally - and often the main features enable easily.

if you take a look at the schems for bally games like barrel-o-fun or lotta fun you'll see references to a 1/2 red button adjust plug. That may help figure out what your mods were doing. Those games didn't have a replay register, but a stepper unit capable of stepping up/down and resetting worked pretty much the same way. Once a game was reset using a coin, the remaining 5 cards could be enabled by the player using the red button or the cards enabled automatically to the extent your accumulated score from the previous game(s) allowed - the 1/2 red button adjust plug configured that.