Nice! Looks like they swapped in a new rear diffuser too.
If you bought the car from them then they will most likely work on it under warranty. Usually if they would void someones warranty over something then they wouldn't take it in trade either.
My guess is it has little to do with the actual shifter and more to do with the transmission. Is the shifter sloppy at all? I know when I put mine into a gear there is almost no movement from side to side yet I've been in others where they are not as tight. If the bottom screws that mount the shifter have come loose it might cause it to bind but my guess is maybe synchos have issues.
