it has always been my experience that the first plugs to go on a small block Mope are the drivers side, then the rear soft plugs, then the right side. I think it has to do with the way the water circulates. It seems to push all the sediment(rust, sand, etc) CW through the engine and it settles mostly behind the soft plugs, left side first, where it accelerates the rotting process. They aren't all hard to replace, except for sure the rear ones, so I'd test all the lower block soft plugs with an awl or a sharp flat-blade screwdriver. If you find any weak ones, I'd replace all the lower ones. If that happens to be the case, I'd pop them all out at the same time, and use a bent coat hanger and garden hose and fine nozzle to irrigate the water jackets thoroughly through the soft plug holes, so you flush out all that nasty sediment. You'll probably be surprised how much is in there. Your cooling system would thank you if it could. If you want to go the extra mile, you can replace with brass plugs, there just a little more expensive, but they are much more corrosion resistant.
