At highway speed, there's always been a certain level of wind noise present.
It's most noticeable around the top of the door/window seal -though hard to pinpoint while driving. I've mostly accepted this and gotten used to it.

Yesterday, however, I was on a long stretch of highway en route to mom's place, wondering as I sometimes do how this noise level could possibly have been acceptable in a new mercedes.
I leaned my head back behind the B pillar to the rear passenger window and lo and behold... it was quiet! Next, I leaned as far right as I could, toward the front passenger window, and again, quiet!

CLUES

When I spray the driver's side door with the sprayer at the DIY carwash, I always get a little water on the driver's seat (though not while driving in the rain). A couple months ago I replaced the window channel run thinking that might have been the issue. Negligible effect.

The door seal feels plush and supple, as do they all. Fairly certain they were replaced by the P/O.

I do know that the P/O had the driver's door off, though it is unclear why.

I suspect that it is somehow misaligned, though I have no way of verifying this.
Is there an alignment procedure, or set of measurements I might check with a caliper?

This comes to an end now!

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1981 240D 4sp manual. Ivory White.

to check the door seal you can use the dollar trick. Put a dollar between the seal and bodywork and close the door. If you can pull the dollar then your seal is not tight enough against the body.

On my 126 I had to bend the top door frame slightly inward to stop whistling.

You can measure the door gap for consistency against other panels too

I’ll give the dollar trick a shot.

Bending the frame sounds a little severe.

For door components, every conceivable adjustment is listed within the body/chassis section of the FSM. The door itself? Nothing.
There must be a standard set of measurements for this.

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1981 240D 4sp manual. Ivory White.

Slid right out... nice trick.

I wonder if this isn't a door striker issue. Possible they're too far out keeping the door from closing snugly?

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1981 240D 4sp manual. Ivory White.

Look at the door in comparison to the back one. Is it protruding out overall or just on the top? Is the top line of the door inline with the rear?
These things can offer clues. Someone had tried to break in my 84 with a coathanger at some point, so in addition to replacing the gasket I had to bend the door to get the top to seal. Its not as drastic as it sounds. I just put a block of wood on the striker and then pushed on the top of the door while the latch was on the block of wood. A couple of good pushes and everything lined up again.

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1985 300 TD 448K
1984 300 TD 278K

1983 240D euro 240k
1994 f-250 idi turbo 330K
1986 f-350 IDI
1987 F-350 IDI

1985 JD 1050 4wd
1965 IH 3660

Thanks for that.

I noticed that both the driver and front passenger door protruded about a mm or two from the edge of the rear passenger doors. So, I adjusted the door strikers further in toward the cabin until the edges of both front and rear doors were even. I used that strip of trim that runs below the door handle for reference.

Using the dollar trick -the grip is about 50% more snug, though closing the driver's door now requires a bit more force. Nothing outrageous, but not as easy of a close as the other three doors. This is why I had initially adjusted the striker plates as far out as I could get them.

Have yet to road test as dealing with a separate issue...

Anything else I might check?

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1981 240D 4sp manual. Ivory White.