The SR20 never stopped leaking,, untill it got up to altitude, and the airframe warmed up,, it leaked.. there were several instances where the leaking fuel caught fire on the ground from the afterburner's flame... rather spectacular..
If your coil gasket is leaking,, drain the system, buy a new gasket, and use Permetex's 'Ultra Black' RTV sealant, available at good automotive stores to seal the irregular surfaces under the gasket.. tighten the plate gently with many gradual tightenings of the nuts.. let the 'Ultra Black' set up over night..
If you have pinhole leaks in the actual boiler outer wall of the water vessel,, you need to do some serious repair,, cutting out and replacing or plating over the erroded spot...
The heat and pressure will loosen any sealant I can think of... You may try 'JB Weld' or 'Marine Tex' many people have good luck with this product in automotive and Marine applications.. Both are two part epoxy based products.. both can be drilled and tapped for threads after a few days..
If you have pinholes.. drill and tap, use either JB weld or Marine tex as thread sealant, and over the whole head of the bolt,, thread the bolt into the threaded hole... and make an extra large offering when the plate is passed...