Hope you're still checking in here - I'm a newbie, too! My cat is almost 16 years old, and was vomiting and having diarhhea a lot. My vet had me take her off dry food completely, and whenever she has this problem now I switch her to Beechnut baby food. Chicken or turkey only, and Beechnut at it has the least (if any) additives.
Hope all is still well, or better I should say.