It has potential, and a Ural chair would be pretty nice, but it could also be a bit of a 'pig in a poke' without careful firsthand examination. I could replace rear main seals, gaskets, etc if that was the source of the leak, but if it was something more sinister, it could be a substantial cash-sink.
I also don't know why ANYONE would "un-convert" a M-G Convert model, ESPECIALLY if it was for sidecar duty - those Sachs torque converters are extremely long-lived and make the whole experience much simpler, I think.