Not all birds that become symptomatic with the Marek's virus die, they can even "get better" for a good while, it just depends on the form of Marek's that affects them.
While multivitamin drops are o.k. in the water, they provide a low dose.
I'd give him direct vitamins as suggested to see if...
Do you have photos of him or a video of his actions?
For video, upload to YouTube and provide a link.
Your initial thought was ear infection - did you inspect the inside of his ears for pus, debris, mites?
Does he have any mites or lice on the body?
Do the feathers/fluff around his eyes need...