I have an 2003 with about 100,000 miles and have been chasing a slow leak from the lower oil pan. A shop installed a gasket before I purchased the car 2 months ago, and I have installed RTV twice and a gasket once along with a new lower pan without success. I have also installed a new oil cooler seal. The leak leaves a decent sized puddle after being parked for a few days. It appears to be coming from the rear of the oil pan. Oil is not coming from above in the engine.

Any ideas how to resolve this?

 

VQ35DE lower oil pans don't use gaskets, just RTV, make sure to use a high quality RTV, like an OEM (I like both Toyota and Honda RTV, I have also used Permatex Ultra Grey with success). It's best to replace with a new OEM pan or replace with an aftermarket aluminum one (looks like you already replaced the lower pan once). Both surfaces need to be chemically clean, absolutely no old RTV/sealant can be left behind. Use a scotch brite to help remove old RTV and then make multiple passes with brake clean and a lint free cloth around the mating surfaces just before installation.

Although rare, it's possible you have a leaking rear main seal or even a cracked upper oil pan.

Some pictures or more details about how you installed the pan would give others a better idea of the possible cause and solution.
-Icer

 

What Icer said … I’d like to know where the oil leak is coming from (such as pictures)?

This is a ‘bad’ and ‘worse’ situation …

The bad is if it’s coming from the upper oil pan > block connection seal … To do this correctly you either need to pull the engine and get it on a stand and re-seal it out of the car or you need to support the engine from the top of the car, drop the front subframe/front suspension/etc, support the transmission, etc and take the pan off from the bottom of the car…

The worse situation is if your rear main seal is leaking … because that is taking the engine out, taking the pan off, replacing the seal and the retainer and then reinstalling everything.

I’ve done them both ways and they are equally difficult. My suggestion is (if you choose to do this yourself) is to remove the engine & transmission, then detach the transmission, fix the seals/RTV, reattach the transmission and put the engine and transmission back in the car as a single unit. Like I said above, equally difficult and doing the work on an engine stand will yeild better results.