Yes, many have tried to solve this air leak, having partial , if any , success. For example, someone has a web page describing how they made out of fibreglass an assembly of a disc afixed to the torque tube which then rotates inside a fixed molded pocket, thereby trapping the mass air flow somewhat. The offset torque tube mod would be really helpful, but google Nick Ugilini's website...very doable, but looks laborious to me.
I think someone in the CA List suggested that you pay at least as much attention to the "outflow" of cabin air. Find all the potential outflow spots... vents, hell-hole cover, space between right side rear console and hell-hole, etc., and you will mitigate the "inflow". This makes sense because you can't get air in, if it isn't going out.
Good luck. I have the same problem, but am not dealing with it at the moment.