Last week my cars engine started shaking very bad everytime I stopped at a stop sign or red light or wasn't pressing on the gas, everytime I stopped the car would sometimes shut off on me when the engine shaking problem started getting real bad. soon enough when I parked the car and came back I couldn't get the car to start and i'm going on a week now without getting the car to start. I checked my oil the other day and it looks like chocolate milk, someone told me that could be a sign of a cracked motor head to blown headgasket. obviously water is getting into my oil which I know is never a good thing. A mechanic recomended I get some type of block sealer before the problem gets worse to where my engine is completley done where thousands of dollars is need to repair. so with that advice I went to kragens and purchased K&W chemical head gasket and block repair which is supposed to be a permanent head gasket block repair. so in order for the product to work properly I need to drain the radiator, my only problem is I can't locate the drain valve or the petcock to drain the radiator. can anyone tell me where it's located on my 94 corsica and what it looks like and what exactly I need to do to properly drain the radiator.

thanks in advance!