My 1973 passenger has always closed like a vault door - strong solid thud.

My driver door has always been just a tad off the thud. I've been thinking of trying to figure out why the difference. I thought it might be the latch. But I replaced that and nothing changed. I do know that YEARS ago (I've owned this car for 35 years), I did open the door insides and didn't see anything different - except that the passenger side had a plastic liner and the driver's side did not. I can't imagine the liner is making the difference. But I think that shows that someone had been in there before and maybe they removed something?

The window frame is a little off. It needs to rotate counter clockwise just a tiny tad.

But other than that, I don't see anything.

Does anyone know if there are any things that are special that help ensure that solid thud?