If water is just seeping I wouldn’t worry to much about it. Also you may be able to spray some heat resistant paint on the inside and outside of the heat exchanger to help seal it.
I don’t think a very small leak on the heat X would cause an explosion but it may dilute the gas but might not be enough to be noticed .
If the heat X reaches the ignition temperature of the gas it is likely a small flame will form at the point of the leak which would weaken the gas and raise the gas temp going to the cooling rails. Again , it might not be enough to be noticed just depends on the size of the leak .
After the gasifier has been used for a while you will be able to look down in the housing and see if any air leaks have fired up . The heat X should be covered with black soot . If a pen hole has formed and gotten hot enough to catch fire it will be white in that area .