Tom may have something...
If all those cars that lean left have original springs and original seats, then the driver's seat springs would also sag a bit, while the passenger's would not... You'll have to admit, the driver's side seat springs always give out before the passengers...

Still, the tendency I've noticed over the years in springs is more weakness front to back not left to right.
BTW, come on, Hotrod, my other theory has considerable worth! If the build date on those 69s is before the end of January in 69, then they would definitely lean to the left. If after, then to the right. Janaury of 69 is when Johnson left and Nixon came in. Chuckle, right back at you...
