I don't know if you should phone a Vet now, depends on how much he's gagging and I sure don't want to see him choking on
this if it does start coming up
poor little guy sure has had his challenges for sure.
Ask the vet if he thinks you could give him some hairball remedy? I don't see why you shouldn't be able to?....but with all his problems I can understand you being afraid to try something...wonder if this old ball of hair hasn't been there for a long time?