It is worth removing completely, if your glass is out. I had seen a couple of small bubbles around the frame, very minor, when I had my windshield replaced. Once out, there was rust around the whole lip area. This is not uncommon. The body shop was familiar with Sprinters windshield area rusting where the eye cannot see. The molding does not seal like other vehicles. It is supposed to allow moisture to drain is MB reasoning.
After grinding down to metal around the whole lip, and several coats of primer, followed by a couple coats of paint, and another couple coats of clear sealer, I feel confident the next time I need new glass, it will not need all the work it did the last time.
I have trouble understanding the molding not sealing completely to prevent any moisture from getting in there to begin with. I suppose MB has their reasons, but with all the rot our Sprinters are known for around the windshield area especially, there has to be a better way.