I remember seeing a kit that replaced the old lip with a new one. It does involve machineing the cases to smooth stuff out and then I 'think' the new part is welded into place OR it may just be a compression fit like a gasket.
It involved a metal ring but I cannot find reference to it.
The James gasket/foam kit is supposed to resolve the problem. I have also heard of great success with JB Steelstick which is a putty like JB weld so can be formed.
Reading up on the James Gasket kit that might be worth a try.
It totally ignores the lip issue and works to provide a damn good seal between the case and inner primary through a special gasket material. get the kit, make sure both mating surfaces are clean and flat and then have a crack at it. If it still leaks then plan 'B' could be the repair using metal putty option.