I have owned 4 vans to date; including my current 1974 G10 with a Martin double crank sunroof. So far so good and what is so mind blowing I had the exact same sunroof in my original 1974 G10. Never an issue and owned it for years and to date I'm good on mine. Original owner did a pretty killer install with a custom frame around from inside.
When I finally get way down the road with body & paint ; going to do metal work and seal it and hope to have my vintage air.