Leaking coolant from head gasket area and valve

(1) motor oil only smells when its being burned.
(2) the output of the air ducts is in front of the gear shift area.
So, I'm thinking that you have an oil leak in the engine compartment (which may be dripping onto the exhaust system), and the oil has found a hot part of the engine/exhaust, and the smell of heated oil is wafting through the cabin air filter into the passenger compartment through the air ducts in the middle of the dash to just above the gear shift area.
If my theory is correct, you should be able to re-route the burned oil odor by changing the setting of your air ducts by changing the setting from its current setting to a "defrost-type" setting, wherein air entering the passenger compartment comes from the ducts below the windshield, rather then entering through the openings at the center of the console.
Ultimately, your fix will be to locate and resolve the oil leak.

Here's your list of possible culprits for the 1997 Nissan Pathfinder

Priority Action Part Type Cause
1 Inspect - Valve Cover Gasket -- Valve Cover Gasket Leaking Oil.
2 Inspect - Oil Filler Cap -- Oil Filler Cap Damaged or Missing.
3 Inspect - PCV Valve -- Plugged or Damaged PCV Valve.
4 Inspect - Oil Pan Gasket -- Leaking Oil Pan Gasket.
5 Inspect - Head Gasket -- Leaking Head Gasket.
6 Inspect - Oil Pump - divided O-ring or Oil Pump Gasket

If the odor really is gear oil (aka transmission fluid) and not motor oil, then there's a leak coming from the automatic transmission/manual transaxle.
Look under the transmission after the car has been parked awhile, and look for a reddish oil spot/blot/pool. transmission fluid is dyed red just for the purpose of differentiation from other automotive lubricants. You can assist the process of color differentiation by putting newspaper under the vehicle once it's been parked for the night.
Placing enough newspaper may also keep your Pathfinder from depositing a nearly-impossible-to-remove oil stain onto your garage floor overnight.
If you already have an oil stain on the floor, try a spray can of engine degreaser first. Citrus degreaser next.

The valve cover gaskets can be a large job on this vehicle and could cost you $450-490 depending on the labor rate in your area. I would quote 5.5 hours; the rear main seal could be about the same, maybe $100 more in labor time.

I would expect an engine with this mileage to leak some oil... not drip, but seep oil on the hot engine and produce a smell or smoke. Make sure the PCV system is working correctly, use thicker weight engine oil like 50 weight Castrol and use an over the counter oil additive like Engine Restore, which you can buy at your local auto parts store.

Hope this helps (remember to rating this answer and leave some testimonial comment).

The valve cover gaskets can be a large job on this vehicle and could cost you $450-490 depending on the labor rate in your area. I would quote 5.5 hours; the rear main seal could be about the same, maybe $100 more in labor time.

I would expect an engine with this mileage to leak some oil... not drip, but seep oil on the hot engine and produce a smell or smoke. Make sure the PCV system is working correctly, use thicker weight engine oil like 50 weight Castrol and use an over the counter oil additive like Engine Restore, which you can buy at your local auto parts store.

Hope this helps (remember to rating this answer and leave some testimonial comment).

theres couple bolts on the valve cover prbly 10 take them off then pull valve cover then new new valve cover gasket on make sure scrap old gasket from valve cover and head so not to have a leak put all back togethor

use a mirror and trouble light , clean the engine and let dry the install a pressure tester, you should be able to locate the leak

The valve cover is located on the top side of this engine. It encloses the upper Cyl head that has oil spashing aroundin it from the valve train. If you have a coolant leak, it is either from the head gasket or the coolant block off plate in the back of the cyl head just under the Brake Master Cly. I hopes this helps answer your questions. Craig

this is oil from leaking valve stem seals

I hate to say it, but it definitely sounds like you have a blown head gasket. Overheating and white colored, "sweet" smelling smoke are both telltale signs of this. If it started overheating first and the white smoke came after, then you will need to have your cooling system inspected after the head gasket is replaced.

Are you adding coolant?
Yes ......means it's going somewhere.
Fill the coolant tank to the top...right to the top....leave the cap off and run the engine.
If you see bubbles you need a head gasket.
The intake gasket is another source of coolant leaks and at this area the coolant can be sucked into the engine and produce a white smoke.
Does the car run rough at the first start in the morning....could be antifreeze burning off in the cylinder or area that was leaking overnight meaning cyl gasket or intake gasket.
Look at the rear head to block area below the exhaust manifold.
Is there any trace of coolant or stains of coolant......yes means head gasket time.
Pressurizing each cyl at a time with air with the valves closed in that cyl will quickly show the location of the bad head gasket with bubbles coming out of the fill tank on the bad cyl (s).
Head gasket leaks don't always mean milky oil.