Oil exchange

[Zigner]

If the oil pan drain plug was loose over several months there would be a major puddle of oil under where the car was parked each day. Too bad OP didn't notice it.

That's a good point. It's possible that it came loose (and then fell out) over a much short period of time, but how would that be the repair shop's negligence as opposed to, say, a failing plug bolt? (Rhetorical question.)

 

[welkin]

Well if the oil change is being preformed by a repair shop or speedy oil change shop and the car is up on the lift, when the oil is drained out you first replace the drain plug hand tight. Then you put a wrench on it and tighten it up. Right? So what would happen if the attendant got distracted and forgot to tighten the drain plug.

Over time and from engine vibration the plug starts to work it way out until it falls out. I think that would be a likely scenario attributed to the shop's negligence. But how do your prove it?

 

[PayrollHRGuy]

Over time and from engine vibration the plug starts to work it way out until it falls out. I think that would be a likely scenario attributed to the shop's negligence. But how do your prove it?

Considering the time span involved you don't.