Check all vacuum hoses and fittings
9 year old vehicle may be wise to replace all hoses one at a time You can get a vacuum pump to test vacuum operated motors under dash
Probably a vacuum leak
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.
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.
You probably have a vacuum leak. Check under the hood for a disconnected vacuum hose.
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 serious vacuum leak could cause that.
There are numerous possibilities. You really need to have the cooling system pressurized to determine what is leaking.
A vacuum leak on a 1999 Ford Ranger can be located using an automotive stethoscope. It can then be move around the engine to detect the sucking noise of a leak.
Once a heater core starts to leak, the only remedy is to replace it.Luckily it appears to be a pretty straight-forward job on the Windstar - the heater core is at the bottom of the center of the dashboard - remove the ductwork and some of the trim pieces to expose the heater core compartment.Of course, this is after draining the engine coolant and disconnecting the heater hoses in the engine compartment.See "Related Questions" below for more...
Find where the leak is. Then seal it. The sealing may take different forms depending on where the leak is.
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.