Parked outside you can leak 6 quarts of oil on the ground, and over 10 years, and there won't be any trace of it. A rust hole in the pan could easily empty the pan over 10 years.
Microscopic bacteria actually will eat petrochemicals over time, that is what happens to oil spilled in the ocean by off shore rigs when the leak millions of barrels into the ocean.
As I said, take it out and inspect it if you really want to preserve the engine, If you don't really care about it, roll the dice with flushes, etc. Just like Dirty Harry said, "Do you feel lucky"?
The thing is, if you spend time and money flushing the engine out, put oil in it, only to find a pin hole due to rust from the inside, now you're back to pulling the pan anyway, unless you want to use an epoxy (JB Weld) to stop the leak. Lots of ways to go, but many are sketchy, and you're guessing, and testing your good fortune.
I'll add that I have been down this road before, and tried the cheap, easy way, and it cost me money, and time. So speaking from someone that has more bad luck than good, I'd have a look see inside.
Ya ever notice that every time VGG does one of these find a car, get it running, and drive it back home, he either doesn't make it, or when he starts running the car on the road, (after his low dollar "Restoration"), it has a blue cloud behind it? Roadkill has about the same results, sometimes they get lucky, and all the stars, and planets align, but I see more failures than successes.....
