For a 235, the usual suspects are a cracked head, bad head gasket seal, possibly, though a bit of a stretch, a cracked block. If it was a 216 you could add the seals on the copper oil line that runs through the block. Have to agree with 52 Carl, take it in for testing. I have gone through this with several heads, The guys I go to pull all the valves and magna-flux the head, check the guides and seats and clean out all the junk inside. They also re surface it for a good seal. It is worth the effort.
