You might want to get some longer probes than an allen wrench to see the extent of your problem. If you've pretty much got it all, maybe filling from the slot will do. We'll see what others say.
Yeah I guess that is the thrust of my question - how deep does it go before a recore is needed. Someone told me I could dry it out with a light bulb, but that was before he knew the extent of the rot.
When you filled your void, did you do it from the edge or did you drill a hole through the deck into it? I am guessing the former?