Cracked head...my old '90 2.3L had that symptom after it overheated once but still ran fine. I never pulled the head but I'm convinced it was cracked because it was always loosing coolant and the coolant was all brown and gross.
It happen to me and it ended up being a cracked block!
Cracked block you get OIL in The Rad.
Blown head gasket or intake gasket is usally water in the oil.
But I have be known to be wrong before.
Like Rick 91GT said Do a leakdown and a compression test. Then let us know what you found.