I was under my car changing my oil, when I noticed on the driver side of my engine what looks like oil buildup. I looked on the top of that area and found the same build up. Its not wet but greasy like dried oil. These Pictures are from the bottom.

Someone told me that look like thy transmission casing, My car is a manual with 125,000 miles

 

looks like the leak is from the transmission case cover, so its probably transmission fluid. doesn't hurt to change the fluid anyway at that mileage.
https://www.scionlife.com/forums/tc-tech-diy-1818/transmission-flush-manual-redline-mt-90-a-59661/

 

Is it normal for the case cover to leak?