I've been trying to hunt down this leak on my brothers 1995 Maxima. The leak has always occured on on the passenger side. I knew the rear valve cover was leaking so I replaced that, but oil was still leaking from another location. I ran the engine while I was trying to spot the leak underneath. I felt confident it was coming from the upper pan so I resealed that but it's still leaking from the same spot.

Sorry for the shaky filming.

So, you have re-sealed the rear valve cover and the upper oil pan? Have you look at the timing chain cover?

found the oil leak. I have the same leak and found out that there are two 0-rings behind the timing chain cover. The part number for the o-ring is 13035ha and 13035h. Here is the diagram of the cover and the o-rings.

Wouldn't the timing cover be wet with oil though? I never suspected timing cover because the drip is coming from behind the motor, not the side. Also, is there any write up on this job? Thanks for your reply.

No, because the seals are behind the timing cover not in the timing cover. That's why the oil leaks down and drips exactly on the oil pressure sensor and the oil pan because its leaking behind the timing cover.

I'll snap a picture of the TC back side tonight. The nearest I have on this subject is the TC Cover Removal Tips that I bet you have already seen.

Since the leak is happening internally, where does it begin to leak externally?

FSM will walk you through pretty much the entire thing. Did this job about a year ago. Took me a couple weekends and several hours each day during the week. A lot of cleaning and removing parts just to get to those 2 o-rings. But yea had the exact same leak and it was those 2 o-rings.

Thanks for reassurance because I don't want to spend all that time on it like I did with the upper pan only to realize that's not the cause of the leak! Does the upper pan need to come off for this job or no?

Pretty much right where your video shows. Mine was mainly dripping off that ribbed hose in your video as well as the bottom of the oil pan, oil pressure sender and the control arm. It was a mess down there and after fixing those 2 o-rings it is dry as can be down there now.

Yes the upper pan needs to come off if you want to reseal it properly because of the half moon seal. I think I did read of some people jamming the seal in somehow but I would take the upper pan off.

How many miles did you guys have on your engines when the o-rings needed to be replaced?

This is somewhat confusing, but I think I get it:

The 2 big slabs are the outer timing cover and the inner timing cover. Oil splashes in that cavity between those 2 timing covers to lubricate the chains etc.

The area between the inner timing cover and the engine block is supposed to be bone dry. The O-ring leak on the engine block finds its way down this normally dry area and leaks out of the back area (oil pressure sensor, filter etc)

Is that correct?

What causes that O ring to fail? Is it simply age? Overfilling of oil? Infrequent oil changes? Or does it have something to do with the oil pump, which these O rings are sitting pretty much right on top of? (The pictures in this thread don't show the oil pump but the FSM pics show it clearly.)

Im a little confused too.. so to replace those two seals on would need to remove (in simple terms) the lower and upper oil pan, as well as the entire timing case, all the belts and pulleys, and all this stuff:

My vehicle had about 160,000 miles on it. Dwapenyi, yes you are correct it is the orings behind the inner timing cover so you do have to remove all the cam gears, timing chain, etc to get the inner timing cover off. It's not difficult just very time consuming. I spent most of the time cleaning off the parts I removed becuase they were covered in an inch thick of grease and oil from not fixing the leak for over a year.You have to drop exhaust, remove crossmember, power steering pump, belts, unbolt ac compressor and I believe alternator, upper and lower oil pan, all pullies, timing gears and covers. Just make sure to set the engine to TDC (Top Dead Center) before removing the timing gears so when you put it back together it's not difficult (FSM explains all this). Also, I probably could have saved a good deal of time if I had a pressure washer to to clean off all the grease so you could probably finish this in a weekend. If you have never replaced the water pump and the timing chain guide tensioner now would be a good time to do those as well while you're in there.