The heat is not working well though, so I think it could be the heater core

 

The heater core isnt going to cause oil to mix with coolant. It's probably blogged judging by what came out of the car. It's the most time consuming job on the car and requires you to remove the entire dash.
On to the real problem, have you run a compression test? Or tried moving the oil cooler at all?

 

I will be trying to do both of those task today. On another note, can you tell me how to remove the plastic boot around the heat core hoses circled in red?
Thanks for all the help

 

Holy friggen clean *** engine bay batman!


its split on the back side i think it just pulls off, its corrugated hose type ish.

 

Thank you!