The screw is not leaking. The leak is most likely coming from the input shaft seal ( a bit further up) or even the tranny vent (on top of tranny body). The screw holds in place a sheet metal shield that keeps debris from bouncing off the road up against the flywheel, etc. The fact that the screw seems stripped may be normal wear if it had ever been removed for inspection ... or perhaps the tranny has been replaced. ??
Is the fluid level normal? It may be overfilled. Does it leak a lot? If the tranny performs well and the leak is easy to keep up with ... I would stay away from tranny repair shops.