You should almost never need to replace a switch, unless it appears broken (contact loose -- although you can repeen it with a few hammer taps; or broken).

Try using a jumper wire. Jump from the R-B wire of the coil to the O-B wire on the coin relay and press the credit switch. If that works (assuming the coin relay energizes) then the culprit is either the score motor switch or the make/break switch on the reset relay. Move the jumper so you skip over only one switch and try again to see where the problem is.

You can make a convenient jumper by soldering an alligator clip to two ends of a long piece of 18GA wire.

If your Total Play Meter advances when you hit the replay button that demonstrates that 2 of the 3 switches are working. If the Coin Unit makes any noise or tries to advance then the problem could be mechanical and not electrical. Does the Coin Unit step up reliably when you push in the advance plunger?

/Mark

The problem might be the coil itself. The internal coil wires might have burnt off the lugs causing an intermittent connection. Inspect connections. Reheat and reflow connections if needed.