Man,
I did the same thing! I R/R my pump and thermostat and saw my leak was coming from a bolt (lower leff looking at pump) that was loose. As my pump had no play, I kept it but have no idea why!
Mine was the last bolt I got to. The far right one. Since I got that far and had already cut the gasket, I went ahead and threw in the new one. This one is a great deal and probably has a lot of life left.