Is there a race track near you? When I have issues that my local vet can't solve (I've recently switched vets and although my new vet is really high on price compared to my old... they are way better at diagnosing things)
I load up and go to west virginia, there is a vet at the track there and those vets are absolutely awesome. they deal with lameness so often because of the horses on the track that they can pick out anything... if there is a track nearby that has an onsite vet, it might be worth the drive....
what a cool idea...I never thought of that!
zoomer, have your friend get a second opinion. I would not have a chiro out until you have a diagnosis. If it is a pinched nerve or something like that, you could make it worse by trying to realign him.