Actually, I looked it up and Petr Korda did win a slam as a lefty with a one-handed backhand (Australian) after Muster won the French - He used lots of different colored rackets, though, so stick with Blue.
Interesting that there are so few lefty one-handers winning slams since McEnroe. Would they have the same problems with righty-forehand to lefty-backhand as Federer does with Nadal? That wouldn't matter as much with serve-and-volleyers. In those days being a lefty was considered an advantage. Is it a disadvantage now with baseline play predominating?