A pinion seal is a rubber or metal ring that is used to prevent oil from leaking out of the differential unit in a vehicle. It acts like a barrier, keeping the oil sealed inside and protecting it from dirt and debris. Full definition
«The rear pinion seals can weep oil,» says Phil. (evo.co.uk)
We've changed the rear axle pinion seal to stop it from leaking. (bugeyeguy.com)
Hello - there are several possible sources of a differential fluid leak: the pinion seal, the axle flange seals, or the rear differential cover gasket. (yourmechanic.com)