I'm so glad Ripley will be able to get into see your regular 'cat' vet for a second check-up. The drooling must be very difficult for you to watch. I too was wondering about his teeth or ulcers in his mouth but maybe it is nausea. I hope the vet will be able to get to the bottom of it. Maybe some baby food would be appealing to him?
Prayers going out for your handsome Ripley.

E.T.A. drooling can also be a sign of a foreign body in the mouth or throat.