I use a small diameter rubber hose as my stethoscope.
I'm out of town right now, but when I get back to the Merc I want to try to add some small blocks and tape on the A pillar to see if I can smooth the air flow around it. Also I may try to tape the back of the front door glass to prevent air leaking into the door and see if that helps. I'll try removing the mirror too.
The problem with these old cars is that all the glass is inset deeply into the body. The windshield has bulging rubber and stainless trim around it too. I wish we had access to a wind tunnel we could use to work on these problems
