This is a psycological issue ^^
You must not try to lubricate those bearings. By doing that you will do more harm than good. The bearing are metal shielded right, but if you try to drop some lubricant, there is a risk that it get in the bearing with fine dust, which will do an abrasive matter and will reduce the bearing lifetime. Best thing to do is nothing.
If it can confort yourself, I have a Castle motor which has more than 200 hours of running with same bearings, I never tried to lubricate them and there are still in perfect shape... The only maintenance I did was gluing again the front bearing in the end bell, with blue loctite (after 50-100 batteries, the factory glue doesn't hold anymore).
In general ways, a bearing can be lubricated only if you can open it and clean it totally.
If you are still not convinced :
http://www.rc-monster.com/forum/show...castle+bearing