Toilets, Sinks, Showers, Tubs and Disposals - Temptrol A Question

We had the knob and escutcheon plate off our Temptrol Model A for quite awhile now in order to do other bathroom repairs. Anyhow, my husband put it back together tonight and when testing it, we saw an obvious leak of water coming from the divertor area. A lot was coming out and streaming down the front of the escutcheon plate. My husband removed the escutcheon and turned the water on so we could see if there was water coming from anywhere. Even when diverting the water to shower (escutcheon removed) we couldn't see any leak of water. I'm looking online now to see what the prob might be. Any ideas guys? I have read that an o-ring can commonly go on the divertor but the water leaks within the wall, not out the escutcheon plate. The tub sat unused for about 2 months. Could that have caused the o-ring to deteriorate? Could my dear husband have made some error in putting on the escutcheon plate when reassembling? I'd like your ideas on problem shooting rather than running the risk of playing with a leak. THANKS!

I would get a rebuild kit for the faucet; strange things can happen when rubber/wearable parts sit in a faucet and not be in use for a considerable time. It sounds specific to the diverter, so maybe this is the culprit itself.