Ohmster

I have a '94 Honda Civic EX with 143K miles on it and have had a problem with getting an air bubble in the cooling system every few days. I would have to open the radiator, top it with water, and refill the overflow bucket. This has gotten steadily worse over the past few months. I found a green streak under the thermostat housing, opened it up, found no thermostat and no gasket, only a thin bead of black silicone. I put in a new thermostat and gasket, sealed it with a thin bead of blue silicone. Found scale on one side of black silicone so that must be the leak. Problem solved...

...no. 3 days later, overheating again. Air bubble in radiator, now it is hard to fill because must cool down engine, open radiator, top it off, run till it gets hot and thermostat opens, see water drop another inch and a half in radiator, top it off again, then close it all up. Now with new thermostat, the overflow bucket hardly ever drops down in water, only an inch or two instead of almost empty now.

I can't find the leak, it is driving me nuts, every day, if I top off the water, by the time I drive 20 miles, I have an air bubble, temp rises, have to shut off air conditioner, and fill with water soon. I need to buy time here, not sure if this car will be okay or not.

Pressure tested cylinders, got readings of 120, 130, 130, & 135. Not too bad. No signs of water or coolant under car. No sign of water from tailpipe. No milky oil or sign of water in oil. I need to stop this leak and do it now. I want to try one or both of two things:

Cut thermostat off so I can install the ring from thermostat to keep gasket shape and reinstall gasket with no thermostat, this way I can top off the radiator without having to wait for thermostat to open.

Add some stop leak to the radiator to see if it helps. What kind of stop leak is good and safe to use? I am afraid of blocking coolant holes and don't want to use any kind of thick goo if possible. What is good, the silver powder stuff or what kind of stop leak would any of you recommend for me to try in this car to cut this coolant loss problem way back or make it stop? Any advice soon please as a good customer is going out of town on the 19th and I have to run his business till he gets back and that is a 20 mile trip each way. My car will not go 20 miles now without getting an air bubble in the radiator.

Please give me some tips and suggestions right away. Thank you.
~Ohmster