I have 2 642s. #1 with lock, prolly bought it in 2004, didn't do anything to it, just shoot it, smooth enough as is.
# 2 bought it a couple years ago, no lock, had extremely heavy main spring(for some reason S&W mainsprings can vary by 5 or 6 pounds these days) I bought a Wolff standard power spring and now it matches gun #1. No polishing on either gun. Very smooth, no misfires, no problem.