Hey, Sorry but I'm definitely not a mechanic, I know just enough to be dangerous

Did an oil change in my 2006 turbocharged Mazdaspeed 6 last night. Went from about 2L of oil in it to 6L. I knew it was leaking oil but my oil change got delayed 1000KM. I suspect the leak is getting worse and worse. Anyways, drove another 3 hours between last night and this morning when I heard a small pop, engine shut off, engine oil pressure light came on, and I had to coast to a stop. I figured for sure it was seizure salad. Or I blew an aftermarket vent in my crankcase. Whatever, its worth like $2000 on a good day. Anyway I come back to it in the daylight and surprisingly it still had oil in it! Mind you it was leaning on the dipstick side being on the side of the road, but full of oil as per dipstick. Motor wasn't covered in oil and no drips underneath in the 3 hours it was sitting there. Outta curiosity I decided to try starting it. The belt turns and all the idlers/Pulleys are turning. But more or less just sounds like a starter whine, does not sound like it is cranking over. I noticed the one idler at the very bottom and front of belt assembly, the idler or rider was spinning but the "Internals" of the idler for lack of a better word was not spinning. It had Three Knubs on it about 3/4" wide and 1/4" Deep. I'm not sure if this is something like a solenoid that needs to activate to turn something internally? Sorry, again, not a mechanic.

Let me know what you think! Is this worth pursuing to maybe get another 20,000 km out of it? I use it for work and its pretty beat up but if i can fix it for under $500 I would be interested. Or am I in for a nightmare on a beat up $2000 car, even though it appears to not be seized and have an intact crankcase.