Rear Crankshaft Oil Seal Broken But New

The engine oil was leaking and the mechanic said it's because of this seal. I bought a genuine one and he replaced it. After a month I had the oil light in the dashboard blinking few times at starting the engine.


I checked the oil level with the dipstick. It was below the minimum. I added oil and drove to the mechanic. He confirmed that the very same seal is broken again. He blames the manufacturer or long storage at the shop. 3 of my friends blame him for destroying the seal at the time of replacement due to carelessness or something.


What do you guys see? Can the justification of the mechanic be valid? I find it weird.