The most common running problem I have seen develop among Superstreets or E-Z Streets vehicles is fatiguing or bending of the copper front axle electrical contact fingers shown in the photos below. The fingers can become bent upward, particularly if someone has pushed down too hard on the vehicle while playing with it. If cleaning wheels, rollers, and track does not fix a vehicle's poor-running problems, my experience is its nearly 100% likely this is the cause.
The fingers can easily get bent to where they make poor contact and the vehicle runs erratically/poorly or not at all. This is never an issue with the new WBB sedan (a totally different design that does not use fingers) but potentially is with all other types.
The fix is straightforward, if requiring of intricate work with a very tiny screwdriver: remove the copper finger piece and bend it back flat along the portion between the red lines in photo #2.
On some vehicles, like this early vintage truck (top two photos), this copper finger set can be removed without removing the axle bearing retainers (blue arrow points to one) or disturbing the axle in any way. But the design of the front axle and copper piece varied slightly from vehicle type to vehicle type and over time within the same vehicle type sometime. On many, you find that a central single-piece axle retainer must be removed to free the copper finger set (third photo, chassis from a short bus bus). There are even variations on that design: I have seen a few where this central piece is a two part unit with a total of four screws to be removed. Those in particular allow a lot of up and down play and this problem is very common. Regardless, the drill is the same: remove it, straighten it flat, inspect the bearing/axle retainers for bending or damage, and re-assemble.
NOTE:
The installation of a supercapacitor "electronic flywheel" will make a vehicle much more tolerant of poor connectivity due to this problem, but particularly if it has two traction tires (like the vintage truck at the top) it has to have enough connectivity: so if and when you have it apart to install one, you might as well check and repair this, too.
