Thanks for all the suggestions. Here is what I did and how it turned out: (1) for the cracks around the circumference of the bulb, I went with Permatex Rubber Sealant, stuff in an orange tube. I compressed the bulb in a vise and smeared the goo into all the cracks and splits with a toothpick. Let the bulb return to normal shape and sit for 24 hours. Voila! No air leaks and the bulb compresses with some flexibility at the seam. I think I am happy with this choice. (2) for mounting the bulb to the aluminum flange, I decided to go with Pliobond, a flexible type of contact cement. One coat on both parts. Let dry. One coat on aluminum and let it get tacky. Then fitted together and shortly thereafter fitted bulb and aluminum to its bracket and tightented the holding nut and washer. Let sit 24 hours. It all worked and there is no air leakage. Hope it holds up!
1959 M-B 220S cabriolet