The best way is not to mess around with the "seed". If the seed was not set, it defaults to 12345. It's the start run number that you'd want to use, rather than the seed. The seed alters the sequence of random numbers that are generated, and the start run number tells you how far that sequence you are.
The easiest way is take your full 100 run monte carlo results, switch to Detailed view (rather than Yield), and then over the particular run numbers that failed, do a right-mouse-button->Create Statistical Corner. This will then add into the corners the specific runs which you're interested in.
Then if you run in Single Run, Sweeps and Corners mode, and have the corners enabled, it will re-run the specific monte carlo points that you're interested in - making it easier to debug them.