Hi still looking then. Oil can leaks from any where their is oil in the carand most cars has they age tend to leak from somewhere .
Some times oil can be split during filling and topping up and run down the engine ,however darker oil leaking would most likely be coming from the engine some where like the sump or sump bung /plug, oil presser switch and any other place the engine has a gasket, rocker cover , just by simply not having been sealed or tightened up correctly.Generally if the rest off the car is clean you can determine what part of the car its coming from. And may not be to big a issue .The problems come when a engine starts to use or burn oil and you do not keep on top of this and allow the oil level to go to low. And also be aware you can overfill the engine and cause other problems and the engine will force oil out .
I understand your caution ,can you find a person to do a pre purchase inspection for you ?
Any car can have problems even new ones .
I would think a problem you can see would be easier to fix than one you can not ,and would put you in a better place to negotiate on price .
I always allow i bit extra to sort out the car after its purchase and nearly always have to spend on it afterwards to sort out the problems left from the last owner.Buyer beware
Good luck hunting.