Roomba's power system has always been a problem - the plastic cases just don't seal well, allowing dirt and fibers to get in and ruin the job. Penetrating inside the case for cleaning and lubricating is possible, but not so easy even for mechanics. If that old drive issue is causing your Roomba to shake and shake, replacing these nodes will likely solve your problem. Replace the brush assembly and battery and clean the old machine and it should run like new for a lot less money than a replacement.