I agree, ask the vet for an honest, unfiltered prognosis. If you don't think your current vet can give you that, then a second opinion is a good idea.
FWIW -- all of my girls have dripped when they were happy, not as a sign of pain or unhappiness so the dripping could be for that reason.
His leg also must be at least somewhat atrophied, that will cause a muscle loss which will make him look thinner.
Sending lots of hugs and good thoughts for you and your boy.