The outer boot is actually cracked and broken open in one spot.

I'm assuming the only way to take care of that is to replace the boot entirely, which means taking the driveaxle off the rear arm (the blue bolt that goes thru the middle of the rotor)?

If I'm already going to those lengths, should I just replace the inner boot too, inspect the joints (inner and outer) and lube them up?

I've driven the car for two more days now, commuting to work, maybe 45-50mph average, 90 miles round trip - and I have yet to hear (or feel) anything out of the ordinary. It's almost like it's the high speeds at long distances (75mph for 2 hours) doing this, somehow.

Is the cracked/broken boot maybe causing the lube to escape, via centrifugal force?

I have been working on my 300SD that's been sitting around (was able to get the stripped crank pulley bolts off and pulled the seal spacer ring off eventually), and was hoping to at least get that working for a few weeks before mucking with the wagon again.