Causes for Drooling Cat?

My 8 year old Siamese cat has started drooling for the last few months. He is a totally indoor cat. There have been no changes in anything, he eats only hard cat food and doesn't even like treats. His teeth seem to be fine and he doesn't have bad breath and has always had his yearly shots on time. If anyone has any idea why he is doing this I would appreciate any info.

By J.L. from Birmingham