If this is a just fitted - I take it it is - tranny then with the fluid at such a low level I'd be inclined to ring the guy before doing anything. Once it's refilled there's nothing to see so he can wash his hands of it. It seems likes there's been a monumental stuff up by him so I'd be onclined to show him as it is. That might mean he comes to you or flat bed it to him - at his cost. This then secures your warranty now and in the future.

