Need help 1994 D15 leaking oil onto exhaust

Alright this is what's happening. About 2 months ago my Civic start leaking oil I couldn't see exactly were from. So I tried leak seal and that worked for alittle while. Then the oil pan gasket started to leak, I replaced that again it stop for alittle while. Now it's leaking from behind this kinda squarish canister on the back of the motor next to the oil filter. What is it and how do I replace it? When I took the bolts out it would only twist a quater twist in either direction but wouldn't pop out. So I was affraid to force it. Can anyone help me solve this problem?