Don't blame the shop. The oil change is sooooo routine that it is usually given to the rookie OR sometimes the "expert" in the shop figures "Hey its just an oil change" and does it half-assed while he is doing (or thinking of) something else.

So continue to take your car there they probably do the more complicated stuff really well. Oil change? Get a ramp and do it yourself, its a piece of cake like you found out and you can be as anal as you want to be about it 'cause its your car

For what its worth I have never checked the housing after I take it off. But I will now so thanks for the heads up.