That rust is pretty superficial. It will clean up easily and good prep and paint will eliminate it forever. You can see remnants of the sealant in the groove, the sealant is only meant to keep moisture from entering the driving compartment. This aspect is particularly important for the electronically sensitive later 463s. The problem with the design of the windshield lip and seal is that moisture is trapped under the seal. When I pulled the glass on my G320, we media blasted and primed and repainted the metal. there was signs of a prior repair, but all the metal was very solid.
I reinstalled with a butyl rubber sealant (3M 08509) designed to keep the driver compartment dry. Once the glass was fully installed and dry cured 4 weeks this summer, I injected Sikkaflex 220+ all around the glass to rubber seal and seal to metal frame. My primary goal is to keep moisture out of the under gasket area and obliterate that space as much as possible. It is worthwhile to replace your windshield every so often due to pitting and visual distortion. I am not particularly good about that as it is just one more thing. However, when I do my glass, I try to preserve the longevity of this area as it seems to be a failure point for almost every model of vintage steel bodied vehicle.