If you're doing that with the engine in the car, I don't envy you a bit! That can be a real nasty job with all the gunk that will spill out of the block (and on you if you get close enough while you knock the old plug out). As mentioned, if one steel plug is rusty and leaking, the other probably aren't far behind. I'd pull the engine and replace them all, and do any other seal that needs it. Otherwise, you'll replace this one plug, put in new coolant, and then next week you get to do it again on another plug.....and then another. Eventually, one in the rear of the block will go and you'll have to pull the engine or transmission anyway. It sounds like a lot of time and effort to pull the motor, until you figure the time it will take to do each one individually. With the engine out, freeze plug are easy to install. In the car can be a real B**ch to get a good angle and be able to drive them in straight. As mentioned, go brass and you'll never have to do it again.
