Disabled is OK, unless you had them enabled and then disabled them. The AV has know to leave files behind. Did you make any of the disaster recovery files, under maintance?
We had another user come through here a while back having the same problem going from v3 to 4. Andy and I got into a discussion as if it was OS Space or data space. But don't recall the resolution. Do search on Guardian, or "clear log" There are not that many threads on the Guardian units. When I get a chance I will see if I can locate the thread.
Once you get the data backed off, the best way would be a clean install. Then the free space is not in play. Due to age of the unit are you going to be installeing new HD's and bring it back online? The OS supports very very large HD's, one users has installed 4 x 750's. I would also open it up and do some cleaning, its amazing how much dust these collect.
edit: Located the other thread, was not a resolution. But here is the link to bring you up to speed on what we discussed
http://forums.procooling.com/vbb/sho...light=Guardian