Update on this one - it was the voltage regulator that was going bad .. I replaced it with the new $15 one and charging is back to normal now. Much thanks for the help!

One more very newbie question -- when I went to mount the new regulator back on the firewall, one of the mounting bolts still feels loose (spins if I try to tighten it more). I didn't overtighten it to begin with and the holes don't appear to be threaded. So, my question is - how to deal with spinning mounting bolts in the firewall in these situations? I don't think I can get behind there to put a nut on the back, right??? Do I need to go up a size in bolts (It's a 7/16" currently) or are there insider tricks for this ?

Thanks!