If you take your vehicle to an oil-change place: Some years back I worked at one. While many of these places (the "10-minute quick-lube" type) only bother to drain "most" of your oil while they are wiping off your old oil filter so it looks like they actually put a new one on, the place I worked at at least tried to do what the customer was paying for. I say tried because the owner felt that each team of two employees should be able to do at minimum six full-service oil changes per hour regardless of the condition of the vehicle or type (ever try to do a complete oil & filter change, check/fill front diff, rear diff, transfer case on a mud-covered truck that hasn't had the respective plugs out in a decade, check all lights/belts/hoses, replace failed light bulbs, etc. in ten minutes?) - and that was before he cut his employees by 2/3 and sent the second member of each oil-change team to the back to work on other things. But, still, we tried to do the right thing as much as possible. One day I heard the guy in the other lane tell a customer, "I noticed some oil on your oil pan so I snugged all the bolts on it real good." So it is possible that you did everything correctly on the gasket but a well-meaning(?) idiot later over-torqued all the bolts because he saw oil - oil that may not have even leaked from the pan in the first place, lol, because it all ends up on the pan (or points south) eventually anyway due to gravity.