My 1999 path finder is over heating and leaking what could be the problem?

Does it only do this when you have a full or near full tank? The O-ring on the fuel pump can crack over time which will do this when the tank is full or nearly full. You have a bad gasket or O-ring somewhere for sure.

seems to me bad head gasket.
do aRAD leak down test yet?
a tool. that is, or get it done. (all shops know what it is)

if fails that test it has leak , then we find to WHERE net
ground , cylinders , engine pan or to OMG tranny pan.
or to passengers toes (foot wells)
if tail pipe show steam hot engine , bad head gasket, or worse
there is always worse. (cracked block or head or even intake manifolds with water cooling or bypass paths.

or do a compression test ( a tool) 150-psi and up on all cylinders, equal by 10%, if 2 are low side by side, bad gasket tops list.

Path finders are pretty good vehicles. If the drive train has been taken care of, it can last up 300,000 miles. At 100,000 miles, there will be some oil leaks. It shouldn't be puddling on the ground though. (walk away) All cars though, at 100,000 to 130,000 will start needing suspension parts, IE... tie rods, ball joints, struts, ect... It's just about that tie for the mileage that they start wearing out. Not all at once though.

Housing gasket of what pert of the engine? Replace gasket!

adding Freon may not be the answer but will cause unnecessary problems if not done by a specialist. Have an accredited ac specialist look at the problem as the ac may not be working because of a leak in the system. He may have also used the power wire for the radio and so there is less current available to work the ac.

Have an assistant blow cigarette smoke in the end of the line and look for the leak under the dash,
Thinking that goes either to the brake light switch or the heater control

hi try this site its awsome for what you need here is the link hope this helps
http://autorepair.about.com/library/firing_orders/bl-fo-7474.htm

Charge the system with a leak finder. It comes with yellow lens glasses and a blue light. The chemical will glow when the light is shinned over it and your wearing the glasses. Leaks often occur where hose connections are. Replacing the orings usually does the job.

What's probably happening is the weep hole on the water pump is leaking water. The weep hole is a warning sign that the water pump needs replaced. You don't have any heat because the impeller in the water pump is no longer circulating water.

Sounds like you need a blower motor resistor. It has bad paths between the 1 and 2 speed circuits.