Welcome to the Werkz.
I'd start by taking it to a specialist transmission shop and see what they think. It may be that something bad has happened, or it could be some piece of rubbish has made its way to somewhere nasty. They may be able to flush it through, change the oil and filter and away you go, or it may be a new transmission, but at least you'll have a second opinion.
Good luck and let us know what comes from it.
Riding in style