My '72 GS came with a block heater. We pulled the engine and it sat on the engine stand for 2 weeks. At the time, we replaced the rear main seal , timing chain, head gaskets, and other gaskets & seals, etc. + block & manifolds repaint. Reinstalled engine and reattached all the other hardware. Took the car for test drive & parked it in the driveway & checked for any leaks. Found a leak. That block heater leaked because the gasket had dried up and shrunk. Now that was a job & a half to remove & replace with a new frost plug.
I like / hate this theory. Like it because the location of drip puts it at freeze plug and explains why it drips when off as heat would seal oring when it runs. But hate it cause as a person who cleans engine blocks all day some block heaters have to be drilled to remove. So to reflect my opinion I'm gonna like gsstewart post but tomorrow I'm gonna remove the "like"
Update. I still havent found the leak. I topped off the radiator and let car run with the heat on. Checked it every 15 minutes in my garage and by time i checked it at 60 it was off..didnt overheat and no leaks but wouldnt start so i did some checking and discovered my fuel pump went out. Ordered a new one and it will be here tomorrow. Once i install it i will look again..I do know after having to pull the top radiator hose off the thermostat housing to remove the carb fuel line i discovered the housing cover is rusted away at the neck so im going replace that part 2.
Just a thought; the heating element is disc with an O- ring. On some versions the disc is made of a pot metal that can corrode. A few are made with a stainless type metal. The regular freeze plugs are like galvanized. But use the fit to seal them- no rubber ring just a sealer and hammered in. The actual heater element fits in space in water jacket sandwiched between outside of block and cylinder bore with wingnut and screw to lodge the whole affair once seated. Regular freeze plugs are removed by striking plug at sixo'clock and pivoting whereas the plug cam be grabbed at 12'o'clock or cresent wrench at same the jaw is placed and levers plug out. Basically you have to lay directly under leak and see if heater is in last freeze plug bore
The starter is right there so it should have been involved - if indeed it is a freeze plug issue-hmmm was it leaking before removal of air conditioning components. and can you refill cooling system and check if heater can be used. Manual states that cooling leaks have to be check while engine off due to rapid evaporation of coolant/ also heater doesn't receive flow until valve/ temp is achieved. Grab the new heater hoses while you are at auto store and good luck trying to take that tower clamp off
Update. I knew it was freeze plug but couldn't find it. So after some research found out freeze plug behind the starter so after i dropped the starter i seen the leaking freeze plug. Was actually easier to replace then the starter. Took less then hour and didn't have to remove the engine so if you are comfortable with replacing a starter then you can do a freeze plug for a 1975 buick 350 lesabre . Other cars may be the same or different so hope this helps someone one else.
I don't want to be the bearer of bad news, but if one core plug is leaking, the others won't be in any better shape.
