@ flytobecat, smrobs, horselover1 - yes, his left hind is what concerned me. He seems to move it differently, maybe due to his confo? Or to an old injury? I will have it checked out when he goes to the vet. It does not seem to be causing him any pain, and he moves around just fine - you should see him running in his field - so I am not going to bring the vet out just for that reason.
One last video I took today - I promise this is the last. He is moving much freer here, and perhaps it will be easier to judge.
Thank-you to everyone who took the time to look/ give their opinions.