1995 Toyota Camry 1995 Toyota Camry Coolant leaking

Engine Mechanical problem
1995 Toyota Camry 6 cyl Two Wheel Drive Automatic 212 K miles

I've had this car for about 2 years and it has been taken care of well, oil changed every 3 thousand and maintenance done. I just put a brand new radiator in and I noticed that it is leaking. I took it back to the shop and they said there is no leak. I had a toyota camry before and it started to let the water into the oil and other liquids this car had the head gasket break. I am wanting to know if there is some kind of stop leak or sealant that can be put in to repair the leak and make sure this doesn't happen again. Thank you.

Jessica