Steve, the plastic grills are easy to remove. Punch out the centers of the pins, then lift out the outer part of the fasteners. then lift out the grills.
The center panel takes a bit more work to remove. knock out the center pins, same as the grills. the panel has some sticky foam holding it down, so be careful lifting it up so it doesn`t get tweeked.
I cleaned out that area on our 240D. there is dirt that accumulates in there over the years. also good to check out the wiper linkage etc.
Didn`t you have a tree limb come down and hit the rear window or roof on your other 123? that would be a bigger concern than a few leaves.
Charlie