81 SBC 305 runs great doesn't overheat. Trans cooler is separate from rad, flushed the block 4 times and I still have oil residue collecting in radiator. Did a combustion gas analysis on the radiator and it gave me a positive reaction. The colour was questionable but it was yellowish = positive. Again my engine oil is prestine no sign of coolant in oil pan. Car doesn't overheat, radiator is new, water pump is new. I performed a compression test cold today and the highest I got was 168 and lowest was 151. Pretty good numbers. So can It still be a head gasket? I don't want to invest any more time or money into it if the block is cracked.