Pretty nice piece of handiwork there... Looks good.
A couple of things came to mind while I was reading this and looking over the pics...
The opto issue... Series *might* take care of it, but don't forget that LEDs can glow at very low currents. Try a shunt resistor of a few to several hundred ohms, depending on nominal etc. I've had to do similar things for stuff like piezo alarms and the like where even the slightest leakage will make them "complain" continuously when all should be silent. Shunting has always worked better in those cases, should work well here too. If nominal voltage is high enough, maybe a divider approach would be even better. A pot would probably fit the bill nicely and you could find the butter zone between false triggers and reliable hits.
The other, don't forget that failing open is only one of two modes - I'd be inclined to make your auto/manual switches auto-off-manual instead. If they already are, well, carry on then, but it doesn't appear that way, so I figure it was worth the mention...
Steve