Thank you for the suggestion on buying the original wiper inserts - I did just that and finally picked them up yesterday.
Couple of questions with a photo (below).
It seemed very straightforward to replace the rubber inserts - take the old one out, insert the new one in its place. I used to do this on my 2002 E320 4Matic sedan. I had the original blades and inserts on the vehicle, and I noticed a difference between what I took off vs. what I put back on. In the picture the original insert for all three wipers has this metal stabilizing piece on each side of each insert running the entire length of the insert. The new inserts I picked up do not have these so they are much more flexible. When I took the old wipers off, the metal support fell off as you can see below. This made it very easy to thread the new rubber on, and I know the likely answer here, but have to ask - do I re-use these metal "supports"? Why do the factory inserts have them but the replacements don't?
And yeah, as you can see it's pollen season here in New England....!