Im almost sure I have an oil leak from the oil pressure sensor behind the engine, always leaking and wet behind the engine, not leaking from the heads just in mid section. Setup is 87 trans am GTA 350 tpi auto.

its probably the intake that is leaking, that is an area prone to problems.

its hard to tell I washed engine bay today, since I got the headers installed the dipstick is off a bit, but the drips seem to be from the rear upper engine area from the mid to passenger side.
I cant pin point exactly from where, the intake was installed last year on the new engine, hard to beleive its from the intake already.

Do you have a vent or a pcv set up on the engine?

Still factory? if the pcv is old change it.. if it is clogged the intake probably is leaking and failed due to internal pressure. Good Luck

I had the same problem 5 years ago. Oil leaking and dripping from the rear head, passenger side.

Turned out to be a leaky head gasket.

Also, check your valve/rocker cover gasket.

You said that you think it may be coming from the sending unit, but you haven't mentioned weather or not you checked yet. Have you checked?
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You may as well just remove the unit and reinstell it with new tephlon tape just to be sure. It seems to be the easier of the above options, so just do it to rule it out. Should only take you about ten to fifteen minutes.

No havent checked there yet because Im not sure what Im looking for and I cant even see it, I just know roughly where its located, more towards the driver side.

Oh, I didn't realize you didn't know where to look. I have the same engine as you(5.7 TPI). Look on the upper rear of the engine, driverside, right by the distributer. It looks like a bell with a wire conected to the top. If the wire is not conected, there will be a flat blade connector protruding through the top. It is connected to the rear of the engine with a 90 degree elbow between the engine and the firewall. It looks like a bell shaped cylinder, about 1 1/2 inces in diameter and about 2 1/2 inches tall.

hard to tell the exact source without dye, I sprayed engine cleaner all over in the engine bay to clean it and under the car.
The oil is dripping for different spots on the back engine, on the cardboard I left under the car.

If you have no way of determining where this leak is coming from, start by changing the easiest thing. I say begin with the teflon tape(did I spell it right that time?)on the sender. Then check,and if needed, replace the valve cover gaskets. Still leaking? Mike and 88 may be right about the intake gasket. Change it. Its a lot of work, but if your saying you have no way of finding the leak, I think this is what your looking at. Just start with the easiest, cheapest, and least time consuming task first, and go from there.

If you can't find it yourself- go to a professional and have them put some UV-activated dye in the oil and get out the black light to find it. At least then you're not randomly changing parts hoping you hit the right one (think of it this way- if you don't start at the head gasket and work up- you could do an intake gasket then find out afterwards it's the head- how many hours will that have wasted). Another possibility is the rear main leaking- if your only 'view' of this is by cardboard on the driveway- I'd be wary about guessing. For the $70.00 or so it should cost to have it checked with dye, it's probably money well spent if you can't find it on your own.

Eric's right. Just take it to someone and have them check it with the dye. On my car I would work from the top down in this case, just to rule out future problems. I like knowing that everythung is leak free. Since you said you didn't think the oil was coming from the head, and you just had the intake gasket changed last year, and that it was likely from the upper engine, I didn't think the you would have to go past the valve cavers before you fixed the leak. Honestly, I don't think you will have to go further than the sending unit. But Eric is still right. If it did, by chance, turn out to be a head gasket, you would have just wasted a lot of time and money. Sorry for the mediocre advice. But before you take it to someone, please check that oil pressure sender. It is a very simple fix, and if it turns out not to be the culprit, you haven't wasted much time or money.