I've done the flex disk two or three times now, and each time I did loosen the d/s clamp nut, drop the car, roll it back and forth and bounce it to settle the d/s, jack it back up and tighten the clamp nut.
When I did the flex disk last time I also replaced the seal ring that goes on the nose of the driveshaft. After dropping, rolling, bouncing and re-raising, I noticed the new seal ring pushed the d/s back enough to distort the flex disk a bit. This didn't seem right to me, so I actually pried the d/s forward to straighten out the disk before clamping. Can't say with any certainty that I did the right thing, but after a 2000 mile trip it still lives.
I've also found that I don't have to drop the exhaust. If you can get a wrench or flex socket on the plate bolts that are partially blocked by the exhaust, then maybe you can avoid this, too. It's worth a try.
Good luck and have fun under there!
George Davis
'69 280 SL Euro manual