Here's a look at a needed upgrade after driving this Losi SCTE/MIP for the past 8 months. Avid RC offers a huge assortment of replacement/upgraded bearings for your RC. Their website is well organized and simple selection of which RC will tell you exactly which bearings are included in the replacement kit. Kits start as low as $22 for the Losi SCTE. Here's where I got it and some info from Avid RC:
Seals are not that tricky of a thing to understand. Rubber seals offer the most protection from debris entering the bearing but at the cost of a little friction from the rubber seal touching the races under loaded activities. Teflon provides the least amount of friction with great protection but teflon seals are known to be touchy animals while under load, they have a tendency to pop off. Metal shields are your most common variety of shield offered in the bearing market by providing decent protection and low friction.
Revolution (RSZ): Avid invented this seal make up in 2003 to offer the best of both worlds. There is a rubber seal on one side of the bearing and metal on the other. A rubber seal offers great dust/dirt/water protection but at the price of added friction. Where as metal offers almost no friction but will allow water and dust to get in over time once the grease has spread out. Since most cars have enclosed hubs and diffs, there is no reason to have the rubber seal inside the hub or diff since no dust, dirt, or water can get to it. But you still have the protection from the dirt not entering from the outside because it is sealed with the rubber seal.
Metal (ZZ): Suggested use of metal is on high temperature areas such as clutches or on tracks that are always well maintained with light watering in-between rounds or onroad vehicles that drive on clean surfaces.
Rubber (RS): They are becoming the more popular bearing among avid rc enthusiasts because they require the least maintenance to keep up to speed. In 1/8th scale clutches the rubber seal is not harmed if your clutch is setup correctly. We suggest that you use these on dusty or wet/muddy tracks because of their protection. The amount of resistance created by rubber is only slightly noticable in our uses so this is another reason of their rising popularity. Because they block dirt from getting in they also keep the grease from getting out.
Teflon (TS): These are hardly seen anymore and honestly we don't suggest wasting your money on them but if you do we suggest you use teflon inside of enclosed areas such as transmissions. They provide the least amount of resistance but best used in non-loaded situations.