If you are absolutely sure what you are seeing in the filter oil is green antifreeze don’t run the engine anymore until you find the cause. Do a compression check including a leak down test. Get a radiator pressure checker and see if pressure hold or fades away rapidly. Testing will tell you if you have a bad head gasket or cracked head. Good luck.
Note: I just reread your initial post. You have a zero pressure cooling system so you Must isolate the radiator and heater to do any type of pressure test on the block or you will pop the seams on the radiator and heater cores. Compression test will probably tell you what you need to know.
Last edited by Justhorsenround; 04/15/2021 7:33 PM. Reason: Added info.
