MudStop sealing system was designed by VeloLab to ensure better protection for the vulnerable main motor bearing on the Bosch Active and Performance Line / CX motors.
Unlike the Bosch protection seal, MudStop completely covers the entire main motor bearing and outer casing. This stops water and contamination getting past the cover and entering the bearing.
When used with the custom made crankshaft seal, it makes your motor as protected as it always should have been

Full information and instructions can be found here: