2006 1gr-fe with possible exhaust leak at manifold

So I've had issues with check engine light coming on and I've got p0138 and p0157 codes. I've changed the sensors with cheapies from Amazon and still no luck. Then changed those with Denso sensors, still no luck. I also took out the mass air flow sensor and cleaned it well. I have a K&N cold air intake and i just did a thorough cleaning. Within the last 1000 miles i also changed the spark plugs. Apparently the previous owner had the tranny worked on. In doing my online research I found that some folks that had the same codes were able to swap the connectors on the sensorsides and their problem was solved. Not mine . So now I'm looking at a possible exhaust leak at the manifold. On the passenger side there is some black oily spew that is on the motor toward the front of the manifold. Does this mean I've got a possible exhaust leak? Would that cause the fault codes? If so I will at least need to change the gaskets? If I'm going that far should I also just do new headers? If so which ones? I'm looking at the JBA shorty, OBX shorty, or Flow tech Shorty. Of all my research online and talking with techs i am told that it is not likely that the actual cats are bad.

If anyone had got any input, ideas, directions or suggestions of love to hear! Thanks!!!

 

yes fix exhaust leaks first and foremost, as it is cheapest and it is required
to get any o2 sensor to actually work correctly. exhaust leak could be throwing off the air fuel sensor and causing a rich burn, which is bad all around and can cause carbon buildup you definitely don't need

then once all leaks are solved...troubleshoot sensors, but only after you verify no leaks whatsoever, or you are chasing your tail

 

How do you diagnose an exhaust leak? Truck is loud already with MagnaFlo catback exhaust and K & N filter so I dont necessarily hear extra noise. Suggestions on headers? As long as Ive got them off changing gaskets should I also do aftermarket headers?

 

google how to do it, and then decide what tools you have available
to detect leaks, or get the official equipment to sniff exhaust gasses

example: cold engine

http://www.instructables.com/id/Find-an-exhaust-leak-without-burning-your-hands/

I can only recommend OEM equipment back to front, as all this crap is controlled by a toyota ECU looking
for specific parameters from all sensors, and it only knows what it has been programmed to do

you want a recommendation ? fix (whatever leaks, breaks, or squeaks) with OEM

 

Great link! Thanks! I will try it in the morning once the truck is cool.