Almost certainly rear toe. After alignment...
If still bad: diff brace
If still bad: traction arms
If still bad: adjustable toe arm
If still bad: I had a terrible time with certain tires, e.g. G-Force Rival S. The floaty/twitchy feeling didn't stop until I switched to another tire, even with...
It is difficult to determine the smoke's true color from the video. However, it looks very white to my eyes, which is highly suggestive of coolant in the combustion process. I highly recommend you purchase a NOx tester to evaluate if any combustion gases are present in the coolant loop. If yes...
Okay. I recommend trying a bonded washer, but make sure it's made of fluoroprene, viton/FKM, or fluorosilicone to ensure it's resistant to ethanol.
Your washer+oring trick will probably work, but if you want something more permanent this should do the job.