Some help needed finding an oil leak, or maybe just a sanity check.

Ok, a little back ground. Bought a used LS6 long block last year, I trust the guy that it is in good shape but he is no mechanic. He was selling it because he had a 408 LS2 built, not because of issues. The ‘tuner’ that took the engine out took out some of the oil gallery plugs, don’t know why as they were not to do anything with the engine but try to sell it. So, I’m a little uneasy feeling that they could have done something and not told me, but I think I accounted for everything. The front gallery plug, a compression type plug, seems to be holding (the front cover kind of keeps it in place). The rear dumbbell one seems to be OK, but not sure. I assume if it were to move out and let oil leak it would interfere with oil getting to the engine, I’d see a big drop in oil pressure if that were true right? The engine did not come with a pan, I bought one locally. The guy never used it, and he had somehow gotten it second hand himself. I’m not feeling confident about it. But, want to debate what the problem could before buying another pan.

A few weeks after putting it the engine in I noticed some dripping. When I went to the track (road race, but I took it pretty easy) I noticed a lot more oil, and when going around left turns it got a noticeable cloud of oil smoke. I parked it at that point, as it seemed to be letting more oil out. So, as part of the winter mods I dropped the engine and replaced the rear main seal and looked for a source of the leak. I did find the engine oil level sensor was leaking, but not much else. See the photos below.

Now, the new rear main seal looked good when I put I in, it was an upgraded one from NAPA. It looked stouter than the OEM one I originallly used. I put the rear cover on, and drive train, outside the Vette. It all looked good, and did not seem to have any binding or any issues really. The oil pan, the gaskets looked good and I added some RTV beads, and tightened down the oil level sensor.

The oil leak did not happen right a way, it took a couple of weeks to show up. It has the same exact characteristics as when I put the engine in. The oil leak does not seem to happen when the engine is off. I have had a few drip spots in the garage, but nothing to account for the oil usage, a quart a week maybe more. It seems to happen when I’m driving around. The oil leak is located at the back of the engine/pan and a little more on the starter side. When I’m driving it comes out so much it blows back on the header accumulator and the tunnel area, and a little up on the starter. I can smell faint oil burning, but no cloud of smoke. The back half of the lower oil pan is covered in oil but the front is clean. The upper pan gasket looks clean, but of course can’t see the back of it. I pulled the intake on Friday and the top back of the engine looks clean, I was surprised at the amount of oil in the intake, but again not a lot.

Here are the places I think could be leaking:
- Oil pan, cracked but only an issue under load. Is this possible?
- Lower pan gasket, but then it would leak more when sitting?
- Oil level sensor cracked, or came loose again. Stupid me reused the sensor. Any suggestions to keep it tight?
- Oil pan miss-aligned, could it be too far forward and not catching all the oil from the rear cover? I think it is not too far to the rear, the bell housing looks flush. I’m no expert and I could have it miss-aligned, but it bolted up with no issues and looked pretty good to me.
- Rear main seal, but seem to be too much for that, and it looked good.
- Rear oil gallery plug (the dumb bell shaped one inside the rear cover) letting too much oil out, but it should be contained by the rear cover and oil pan right?
- Oil plug in the crank? When I put in the pilot bearing it looked good.
- Dip stick? I was pretty sure it seated fine and it looks to be sitting perfectly, but could it be not making full contact? Still seems like more oil than that would come out of there.

Things I’ve ruled out, at least I think:
- Oil filter, pretty clean on that side of the engine and filter is clean.
- Rear gallery plugs on the sides of the block, both look clean.
- Oil from top of engine (sensors and valley cover) all clean.
- Oil from front of engine, its all clean.
- Oil from the heads, no coolant usage and its all clean.

No significant oil burning, have not seen any smoke when getting on it.

I’m going a little crazy here, I really hope I don’t have to drop the engine again.

Here are a couple of photos of the back of the engine when I dropped it this winter at the time of the original leak. The rear main seal looks ok to me, just a little weeping of oil. To me it looked like the oil level sensor was it:









Am I just an idiot and recreated the issue with the oil level sensor? Seems to me now that I wrote this up that it is more than likely the oil level sensor again

Thanks,
Matt