AS far as your options go sending it in to Traxxas is not a bad one..
At the least you will have a FRESH esc with a 30 warranty
Thier service department is easy to deal with about a 3 week turnaround.
Perhaps the biggest reason is the price point. For $50 you are not going to find a waterproof ESC capable of handleing 16.8v unless you go to fleabay and take a gamble... Even then you'll be hard pressed to find a functioning ESC for that price