Head gasket?
 

My 01 I just bought has a rough idle and the P0300 misfire code. Well after further investigation I have found that the two adjacent cylinders on the front drivers side have low compression of about 60 to 70 lbs. Mechanic said that when he blows compressed air in cylinder some will come out the other. He thinks it a head gasket. No water leaks in oil or coolant loss. What do you think?