Thanks G4F. I've taken the side place off and can manage the repair myself...I think. I've found the spring and stop on brownells but it doesn't say anything about being over sized. Just says cylinder stop, MIM. I know what the MIM is, but are they all "oversized" now...

SMITH & WESSON : CYLINDER STOP, MIM - World's Largest Supplier of Firearm Accessories, Gun Parts and Gunsmithing Tools