i do my own oil changes. i brought my 2015 mazda3 to the dealership for a recall. they did their usual 360 degree check (or whatever they call it) in addition. the service rep said the mechanic found slight oil leaking and suggested that i replace the drain plug/washer. i can see it not being tight. just tighten it, right? but to buy a new one and replace? ??? How does an oil drain plug/washer fail?