What are ways to check for headgasket leak

I would not see any problem with tightening them again. Does the fluid in the radiator have bubbles in it when the engine is running? Any wetness under the car from antifreeze blowing past it? You could try the powdered sealant to see if that slows it down or stops the leak altogether. A nameless car company used to do that for complaints of water usage in the cars...guessing porosity of the cylinder head. Just some thoughts, hope they help. Bob