Electrically this doesn't matter, the prefix indicates the mounting position of the terminal lugs, as viewed from the coil's round end, with the lugs pointing away from you: AE- means that the coils's two lugs are mounted in the two end positions: AL- means that the coil's lugs are mounted in the left and middle positions: AR- means that the coil's lugs are mounted in the middle and right positions.

Not sure what you mean. more info?

Voltage jumped?? there should be constant solenoid voltage at the terminals all the time when the game is on. The voltage drops momentarily when the coil fires.

This is not how you test the transistors. Improper testing can lead you down the wrong path. Read the repair docs....at least this section but reading and understanding the entire document is desired.
http://techniek.flipperwinkel.nl/wms11/index1.htm#trans

U50 is a 7402 is a DIP-14 located very close to the K1 relay. I cannot say if this your problem, proceed slowly and do/learn what should happen on a correctly functioning board and perform some more troubleshooting. The Rottendog MPU is supposedly based on the original schematics with the same designators, so it shouldn't vary drastically from that standpoint.

Always good to check fuses, but that is not the case here. There is not a separate fuse for each diverter, and according to the ops first post, one works but the other doesn't. Power is daisy chained so simply use a voltmeter to check for the presence of solenoid voltage at each diverter. If one doesn't have voltage, most likely a broken wire or solder connection - either at the failed diverter solenoid or upstream from it.

You really can't assume anything, and a "shotgun" approach - just replacing the chip - is no guarantee. You could get lucky, but its just a best guess. There's other components within this circuit such as the pullup resistor off U11, etc.. If you troubleshoot first, you gain information that can better ensure you locate the problem. Use a logic probe, DMM or oscilloscope to trace the momentary pulse that operates this circuit. Usually this is done in coil test mode. You have identical circuits that behave the same way for each transistor to compare one to the next. U11 is a tri-state inverting buffer, so you can look at the inputs in this matter, rule out an upstream problem or not, and proceed to the output side.

3-s2.0-B9780750645829500111-f10-23-9780750645829 (resized).png