I have found that High Temperature Five Minute Epoxy Putty works well sealing the perforations in my stainless Steel Wood Doctor furnace. The trick though is to apply the Putty using a reversed cabinet clamp so that you can get enough pressure to seal off the water leak and at the same time get good adhesion to the metal.
You can't just push this Putty on with your hand and expect it to hold! The first ones I just pushed on leaked and pealed off again!
Cut a square of memory foam and place it over the Putty against the boiler and then push the memory foam almost flat against the side of the boiler until the Putty hardens. After, just peal it off and you're ready to apply another patch.
My Wood Doctor boiler is littered with patches now and they seem like they might hold till spring now that I have applied them with pressure! Hopefully this will get me threw, this, only my forth heating season!
Who knew stainless steel could corrode threw like this!!