It could be that the switches in this score motor stack need cleaning/adjustment. Loosen the screws, clean/sand contacts, and make sure they make solid contact.

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And am I missing something? I don't see the Runway RO on the schematic.

Hi tbaum, currieddog +
You know the "Trough-Switch on Gottlieb pins" - under the apron for the ball to rollover - to actuate the Trough-Switch (for to actuate the P-Add-Player-Unit-Relay)". Some Williams (end-1960ies ?) ALSO HAD AN Trough-Switch for to actuate the Ball-Index-Relay --- here https://www.ipdb.org/showpic.pl?id=989&picno=53301 a picture of "what we are used to": NO TROUGH-Switch - BUT some Williams have a Trough-Switch there - maybe the Williams Lady Luck (?)
Here https://www.ipdb.org/showpic.pl?id=1404&picno=71631 I see a bent wire (to actuate a switch) on the right, way up in the launching lane --- on the bottom, on the right in the picture I see "Lady Luck has a gate". I looked in the ipdb-schematics - the gate opens when the Player-Bust-Relay is pulling - and the open gate is made to close when the Player-Bust-Relay is not pulling or made non-pulling and the Player-Reset-Relay actuates --- not a playfield switch to close the gate, hmm. The wiring (schematics) of Player-Bust-Relay is complicated --- in the schematics at DEFG-7 the Player-Reset-Relay with switches is shown - one switch is called "Trough Sw. (P.F.)" to actuate the Player-Reset-Relay - hmm, where is the switch mounted (?).

tbaum - You have a "sometimes fault (which are non pleasing)" - when the fault shows up: At the time the ball rolls under the apron from Outhole to shooter alley ? - or at the time You launch the ball and the ball rolls (up in the shooter alley) over the bent wire (just before entering the playfield) ?

Do You have some 24VAC-(SteveFury)-Testlight(s) ?
See here https://pinside.com/pinball/forum/topic/reading-gottlieb-schematics#post-2634425 made of two (cheap) 12Volt car bulbs - one behind the other, 12Volt plus 12Volt sums up to 24Volt. See the JPG here --- 24Volt-Test-Lights.
Only look at the JPG here https://pinside.com/pinball/forum/topic/olympic-hockey-on-off#post-4808166 - how I like to use an Test-Light on "seldom faults" --- the Test-Light has long wires, is hooked-on a specific coil --- long wires coming out through the open coin-door, Test-Light (insulation !) we may lay on the apron --- we play and keep an eye on the Test-Light and when the sometimes fault shows up - what did the Test-Light do ? With this setup we can play and learn about the fault.
Do You have a Test-Light (or two Test-Lights) ? Greetings Rolf

0pinside-Test-Lights.jpg