I've been off the board a few days, but I just changed out the four drive axle bags and shocks on my '89 102A3. Unless the other bags look great, I strongly recommend doing all four. I also recommend pulling the shocks. It's not mandatory but they come out easily and it opens up the work area. It also makes easy access to all the bag and brake air lines, valves, and connectors. In case you want to leak check and/or modify as I did. I found a DD3 leak I didn't know I had.
On the front drive axle bags you will need either a crowfoot wrench or a heated and bent wrench to remove the 1-1/8" nut on the air line port. As you've probably observed, you only have 4" of work space and the nut is mostly hidden by the upper bag support. I found a standard open end crow foot would not fit, but a split box end 1-1/8" crowfoot did the trick. The removal of the rest of the hardware is a piece of cake.
One of my copper lines/fittings had been abused previously in the bus's life and didn't want to reseal, so I converted the air bag system to DOT nylon. I used local supplier but I was told NAPA had a supply of DOT fittings. I like this place and their prices are equivalent to the local shop here that takes forever to order something (we don't have a NAPA store close by). http://www.valleyhydraulic.com/store/shopdisplaycategories.asp?id=353&cat=Push+to+Connect+Fittings
By the way, MCI wanted about $162. per bag and they were out of stock. I got four bags at Mohawk for $103. each. Similar savings on shocks from Mohawk.
Good luck, Chuck