The outhole relay hold circuit may be failing. On the outhole relay find the red-brown wire connected to the relay hold switch. This wire will also be found on score motor switch 5B normally closed switch. Clean and inspect switches for positive connections.

Once you find the coil in question on the schematic look around and find a normally open switch with the same name as the relay. The wire leaving the switch is the hold circuit wire. Sometimes a hold circuit wire will be shared with other relays hold circuits. In this case it’s the 500 point relay and others. The hold circuit release switch will usually be a normally closed score motor switch or a normally closed end of stroke switch on a step unit depending on the circuit.

Solenoid and relay coils are often listed in tables on the schematic that indicate where on the schematic each one is. In this case the Outhole relay is at E-16, referring to its grid location (like in the game Battleship).
Grand Prix Outhole relay (resized).jpg
Once you've found the Outhole relay coil, there are two main circuits that can power the coil. In this case the upper circuit, which involves the Outhole switch and other switches on the Alternator, Bonus Unit and Score Motor, is what fires the Outhole relay initially. The lower circuit with switches on the Outhole relay itself and the Score Motor is what keeps the Outhole relay active until the Score Motor switch at 5B (late in the Score Motor cycle) opens.

/Mark