This is a bottle of Traxxas 100K Weight Diff Oil (.7 oz / 20cc) with fill nozzle. This thick viscosity oil can be used to stiffen up differential action in many RC vehicles. Diff oil this thick is often used for center differentials.
Traxxas Part 5130 - Oil differential 100K weight
Traxxas 5130 - Differential Oil 100K Weight
Traxxas 5130 Oil, differential (100K weight) NEW IN PACKAGE TRA5130 TRA1
Traxxas Differential Oil (100k Weight) (20cc) (5130)