Oil can leak from any number of bad gaskets or loose bolts. Clean the engine at a car wash, getting as much grease off as possible. Watch closely for a few days over the entire engine, even under it, to try to find the leak.
A serious vacuum leak could cause that.
Probably a vacuum leak
There are numerous possibilities. You really need to have the cooling system pressurized to determine what is leaking.
There are several posibilities. It is common for the oil pan gasket to leak on that vehicle. you need to pinpoint where yhe source of the leak is. If it is wet at the top end then it is likely the valve cover gaskets.
A blocked heater hose could cause a leak. A stopped up heater core could as well. Or the connector in the Windstar could be cracked.
You may just need a tuneup. Could be a number of things. Dirty fuel injectors, vacuum leak, etc.
vacuum leak
The blend door is vacuum controlled. Any vacuum leak in the engine system can cause the door to not function properly. Check this system first. The door could be physically sticking but a vacuum leak is a more common problem.
Take it apart to determine the cause. Only then you will be able to fix it.
engine oil leak
You probably have a vacuum leak. Check under the hood for a disconnected vacuum hose.
The Windstar transmission could have a seal that leaks worse as the transmission gets hot and the fluid is under pressure. Go to a car wash and clean the transmission good. Watch for several days to see where the fluid is leaking from so that you can find and fix the leak.