Inspect any used airweight carefully before purchase. Open the cylinder and look at the frame just under the barrel (where it's thinnest). Over the last two years I've seen 3 (a Model 38 Bodyguard, a Model 37 and a Model 12) with cracked frames!
IIRC, this was traced to over torquing the barrel on installation. But whatever the reason, there is no warranty for this, because those frames are no longer made/in-stock and the guns in question were made before 1980 and pre-date the excellent warranty that S&W has now.