Head scratcher oil leak

I have a 2006 dc SR5 4wd, 205k miles. Just bought the truck 2 weeks ago and have been doing some repairs (brakes, rack and pinion, transfer case actuator, valve cover gaskets, spark plugs, MAF sensor, LBJ, etc.)

Im no mechanic and have just been learning off of YouTube but everything has been going smoothly.

No leaks were present before I started doing repairs on the truck, which I believe the oil levels were so low there was nothing to leak.

I'm being stumped by an oil leak after I changed out the front diff fluid.

Truck had not been taken care of and all oils/fluids were pretty black. So after valve covers were fixed I went ahead and changed the engine oil finally. 5 1/2 L came out pretty black. Put in the right amount and kept doing repairs.

Then I changed out front/rear differential fluid and transfer case fluid all to the service Manual specs. Went on a drive and came back to realize that there is oil coming from under the truck near the flywheel housing under cover area and/or the front diff rear seal where the front driveshaft meets the front diff.

My initial thought was to change out the breather hoses which were corroded shut and that way the diff fluid pressure doesn't build up and exit out the seals. Did that and still have the leak. I have also changed out the breather valves behind the engine and firewall.

The flywheel housing under cover has a little gap underneath it to which I then thought, oh man that can't be right, so I stuck a little straw under the gap and saw there was oil on the straw, so maybe that's where the leak is coming from. I don't know if the flywheel is suppose to be covered in oil or not or if I have a rear main seal leak.

Again it was not leaking once I changed the engine oil and took it for a drive, before I even touched the front diff, only after.

Im hoping someone can give me further clarity.

 

You were working on the top-end with the valve cover gaskets. Did you check the back of the block to see if maybe you have some oil coming off the back of the heads at the half moon plugs? I'm trying to visualize in my head if it could end up down that way, but I'd be looking high up on the back of the block to see if you can see something, and if it truly just started, that's the first place I'd go to look. Especially if following YouTube, there are a couple of valve cover change videos that absolutely show you the wrong way to do stuff on that topic!

Do yourself a favor, hit this thread: https://www.tundras.com/threads/so-you-wanna-buy-just-bought-a-1st-gen-tundra-eh.115928/

Look about 4-5 paragraphs down. See all those links in a row? Click on the Service Manual link. Download the one for your year range. Use that as your reference. Seriously.

 

What kind of engine oil did you use...dino or synthetic? If you used synthetic, it's possible that this may be the first time (unless you know differently). Synthetic oil has a smaller molecular structure (or so I'm told) and it tends to find leaks where regular oil didn't. In such case you may consider @shifty` approved

$20 AT-205 Re-Seal Stops Leaks, 8 Ounce Bottle

AT-205

 

Well I Narrowed it down to the front differential rear seal where it meets the front driveshaft. Took it to a mechanic to get a new seal, now I'm being told that the pinion is moving around in there after they removed the driveshaft and it is not supposed to be. They are saying I need a new front diff all together which isn't hard to fathom because when I was changing out the diff fluid it was black sludge. Does anyone know if the front differential is floating or not? thank you