I did my 68A windshield frame about two months ago.
It had delaminated glass, lots of 50 year old silicone sealer, and the groove was a combo of glass, rust, and the seal. I first used a hammer to beat out most of the old glass. Then, I used a putty knife, an ice pick, and a cut down screwdriver.
I did it over a few days, mostly lots of elbow grease, and as the top of the photo shows, lots of fine crud and stringy silicone were still showing up after a day plus working on it. ...then I had the frame sandblasted. Afterwards, my painter saw all the rust through in the channel and suggested I buy/find another frame. My biggest concerns were the bulging rust blistered areas that had been in the frame all these years. When I started, these visibly bad areas looked about the same condition as they had around 1960, so I figured if I clean it up enough, prime it, put in new seal and glass, paint it good; then it should last longer than I will. I was able to get the bulged out rust areas all cleared out and back to pre-rust shape. ..so, I spent another couple days TIGing up rust holes in the channel. It looks pretty good and quite useable now. Just took time and patience.