Thanks Gemmapookie, we were thinking along the same lines but the vet isn't so sure.
His ears were given a really good exam and there doesn't appear to be anything there, plus the abscess is very 'round and mobile' (think she means not attached to the jaw/skull bones).
Vet thinks it's either pasturella or EC, so we have Baytril and Panacur. Hopefully he will start to improve soon. He's still not eating on his own.
He's fighting the syringing more though, so I'm taking that as an improvement, and for now his gut is def still moving.