Need help identifying a problem, Engine Leak

[05Speed3]

When I bought this car, it had a leak. Knowing this, I got under the car to wipe the engine down, with the intention to go driving and see where the leak was coming from. When I was done wiping the engine down, I noticed this:

Spoiler

The dent/hole is up in the top left, with the oil smeared around it.

I would like some help with identifying what is the problem here and, if needed, the part I need to replace.
The engine still holds its oil and drives fine, just have to top it up every now and again.
I think the issue is a leaking rear main seal but would still like a bit of help, thank you.
*edit* Forgot to add that I have a bit of a weird car, it is a 2005 Mazda 3 HB with the engine out of a 2007 speed 3, hence the name 05Speed3.

 

[Easter Bunny]

Rear main seal leaking that much "should" mess up the clutch but don't know what else it could be

 

[05Speed3]

Rear main seal leaking that much "should" mess up the clutch but don't know what else it could be

When you say "mess up the clutch" should I be feeling a slippage of some sort or something else?

 

[Easter Bunny]

I would expect the clutch to start slipping with that much oil coming out of the rear main seal