Oil leak into passenger floor board what is the cause

I would bet if you check your radiators coolant level,it's low! That's probably antifreeze/coolant leaking from the failed heater core into the floor. You probably smell a sweet smell inside the vehicle? windows probably fogging up when heat is turned on? copy and paste the link below..If it is the heater core leaking,probably around $1000.00 to R&R. most vehicles today the complete/partial dash has to be removed to do this job,app. 8-10 hrs labor! https://repairpal.com/heater-core-under-right-side-of-dashboard-may-leak-engine-coolant-488#