I bought a new Roomba yesterday. Sears had the base model 405 for only $129.00, so it was really a no-brainer just to buy a new one. My old roomba has served me well for two years, but it's reached a point where the battery won't hold a charge for more than ten minutes, and it's showing it's age in a lot of small jury-rigged repairs I've made to it. The plastic clips that hold in the rotating brushes broke a while back and I wound up just using screws to hold the whole assembly in place. I haven't bought a new filter since I got the unit, choosing instead just to wash the old filter with soap and water every few weeks, which got the job done.
It seems a shame just to toss the old roomba in the trash. If the battery still held a charge long enough to finish a room, I'd still be using it. It occurs to me there may be some engineering class out there somewhere that would like to get their hands on a free robot for a class project. I'll even pay for ground shipping in the US. Just drop me a line at nobodynovelwriter (at) yahoo.com.