The crankshaft is the part of the engine that helps with the movement of the pistons. It aids with the rotational motion and converts it to reciprocating motion. The crankshaft seal is in the front of the engine and is what helps the oil change directions back to the oil pan. This helps the oil to not leak and is how the oil levels are maintained in your car.

The seals are generally made from rubber, and while it is a simplistic part and design it is important to prevent oil from leaking in the crankcase of the engine. If your seals fail, it can create problems for your car that will damage your engine and be pricey to fix.