Tbh there's probably dogs out there on the worst wet tinned food known to man and they're fine. Just like some people smoke, drink, eat crap and party all their lives and live into their 80's whilst some who do none of that get hit with illness in their 40's. Nothing is 100% guaranteed to happen/not happen. If he's fine on it and you have no issue feeding him it then carry on! I don't get snobby over it like some on the pet forums. :D
If you do look at changing, do it gradually and get him something hypoallergenic like Burns or JWB or even Royal Canin (although some people have said they have changed their ingredients recently to include a nasty ingredient) but RC have stuff that's gentle on tums.