As James Levine winds up another season at the Met and prepares to take the helm of the Boston Symphony in 2004, concerns over his health and ability to do his job are finding a public voice. Persistent shaking and loss of energy have become an everyday part of Levine’s podium demeanor, and his musicians, many of whom stress that without Levine, the Met orchestra would not be the revered ensemble it is today, claim that he is nearly impossible to follow on a nightly basis. Levine insists that, despite the shaking, he is in excellent health, but questions persist about his workload and future prospects.