Something on my frame seeping oil?

Any idea what this thing is? It's on the frame, close to one of the cats (as you can see) and it seems to be leaking a little bit of oil. It's not dripping but the frame around it is oily - you can see it's slightly darker around it. There's another one on the driver's side frame but it doesn't seem to be seeping any oil.



Also, the reason that i was under there was to try to think of ways to attach a plate or something to protect the cat from being stolen. Is there any reason that I shouldn't drill into the frame? the presence of something with a cover on it and that seems to be seeping lubricant makes me wonder if I should be drilling into it or not.

 

That's the frame recall "fix" I'm assuming the "oil" is some type of cleaner or sealer for that plug.

 

I do recall (see what I did there?) that the fix was to fill the frame with some kind of rust deterrent. I wonder if whatever they filled it with could actually leak out, thus defeating the purpose. But I also haven't heard of any 2nd or 3rd gens having problems with the frames rusting internally.

 

I just found this:
https://www.tacomaworld.com/threads/part-number-needed-frame-plug-cap.517334/