Ross, I think its easier to remove the dryer from the bus to work on it. When you get your decissant, be sure to get a kit to rebuild the purge valve as well.
The Bendix website has great info on servicing the AD-2 dryer, as well as a toll free help line that you can get correct advise.
One thing the Bendix tech told me is that it would be better to update to an AD-9 dryer instead or rebuilding the AD-2.
If you decided to persue that route, the AD-9 can be picked up on ebay usually for $50, and then rebuilding it cost comparable to fixing your AD-2.
Also, check the current to the 24V heater on the dryer. Mine was mis-wired (imagine that!) and power was on any time the main dosconnect was on.
In retrospect, I would have bought the 9 dryer, however,my AD-2 works properly now-hope this helps-Chuck Lott