I use to take the time to piss with taking the seals out of bearings or putting them in a bearing blaster to blow the grease out and relube them with lighter oil but in all honesty it's a waste of time not to mention the seals are fragile and you generally won't get them back in without biding the bearing anyway. Seriously just take the car out and put it down on the track and run it, the bearings will free up quickly. I don't clean bearings either, I order all my bearings from Avid, when they get gritty I pitch em, they're a buck. If bearings do need relubed I use drywax products like these.
http://www.whitelightningco.com/products/index.htm
http://www3.towerhobbies.com/cgi-bin...?&P=8&I=LXTMF4