Paul:1) I replaced the pinion seal, tightened the pinion nut good and tight with a 1/2" socket
I'm not sure exactly what's wrong. But, if something changed after doing the pinion seal, then that job, and not the drive shaft support, is probably the cause.
The thing that jumped out at me in your description was "I ... tightened the pinion nut good and tight with a 1/2" socket". My manual lists the pinion nut torque as 58 to 101 foot lbs - I'm a little puzzled by so wide a spec., and suspect that some tightening procedure is called for. Can anyone expand on this? I'd suggest getting a torque wrench, and determining if the nut is tight enough.
On my Alfas, that nut is an odd castle-style. I'm surprised you just refer to a 1/2 inch socket. Is the pinion nut on your car just a regular 6-sided hex?