Oil leak: cleaning and diagnosis help needed

2014 Plugin Prius:
While changing the oil today, I noticed that the area was covered in oil. There were no oil drips on the floor so it is not "yet" a major problem.
The oil leak was from above the pan and filter area, BUT below the belt.

I think it is the oil pressure switch, but I have an almost 100% track record of my first guess being wrong .

Here are a few questions:

1. How can I clean that area? What is the easiest way to clean it?
I was thinking of spraying a simple degreaser in that area and then washing it off. Anything particularly wrong with that approach? Apart from the engine needing to be cold!!!

2. How do I diagnose the problem? I was thinking of using an engine UV dye + black light. Do I also need a borescope?

3. Assuming it is the oil pressure switch, how do I get to it? The manual says I can get to it by removing the front right wheel.

4. Could it be timing chain cover seepage?

Thank you!!!

 

> It is possible the oil filter housing wasn't tightened enough, or the "O" ring was installed in the wrong...
Noooo, I am obviously perfect and never made any mistakes... Frankly speaking, that seems much more likely than Toyota making a defective part.

I'll start with gunk. For any specific areas that didn't get cleaned, I can use brake cleaner while working on them.

 

Any advice on timimg chain tensioner oil leak?
After cleaning the car engine area as well as could, I found oil around the timing chain tensioner. There was no oil around the oil pressure switch. I cleaned the tensioner area again with Simple Green, just to make sure that it is not left-over oil from before. I know I cleaned it earlier and passed my hand around that area as there was no oil earlier.
I'll be more sure after this round of cleaning. I did run my hand over the upper part of the engine in that area to make sure oil didn't drip down from above; nothing coming from above.
I am definitely batting at 100% on swinging and missing with my first guess: I had guessed it was the oil pressure switch and I even have it in my Amazon checkout, ready to go

I am probably going to work on it this weekend. Any advice will help.

 

I have oil around the tensioner with the two bolts and the two 10 mm nuts.
I am now going through the process of verifying my findings a third time.

For the life of me I can’t seem to be able to put the 2014 plugin into maintenance mode.

Yeah, I know I should have posted this in the plugin forum but I made a mistake.