T&T: Antifreeze Leak at Neck of Radiator

[Bob/Myrna Siegel]

Engine is Perkins NA 6.3544 with a coolant overflow tank.  Notice small leak
at radiator cap on engine.  Remove cap, clean neck and replace with new cap.
Leak persists.  Overflow tube is not clogged up.  Have, in past years , seen
professional mechanics peen down flanges of neck but am reluctant to go that
route.  Fix?? or workaround?  Bob Siegel 36' MT sundeck "Shalom" Annapolis