First of all; it sounds to me like leaking under the water pump area would not be related to either blown head gaskets or a cracked block. What leakage in this area usually comes from is either loose pump shaft bearings (which often cause leaks from the pump shaft, since the internal seals inside the pump cannot work if loose pump bearings allow the shaft to flop around), or from debris or old gasket material left on the engine block when the pump was put back on.
Even small amounts of debris left under the pump flange will prevent the flange from sealing when the pump is reinstalled. The pump will also leak if the new gaskets were not coated with the proper gasket sealer when they were installed; or if the pump housing had cracked from being misaligned or overtorqued. On some engines, there are certain critical pump bolts which are required to be coated with sealer before installation; also the pump bolts are often of different lengths. If the wrong length pump bolts were used in some holes, or if there are critical bolts which were not coated with gasket sealer; the pump will leak.
It sounds to me like your water pump has become worn, and that may well have been the source of the original loss of coolant. Whan a loose, worn pump is subjected to extreme pressure (which is what happens when the engine overheats) it will suddenly begin leaking much worse than before. A ten year old pump which leaks should have been replaced; rather than just installing new gaskets. There is a drain hole on most pumps; which will begin leaking lots of coolant when the shaft seals go bad. There is no way to stop such a leak without replacing the pump.
Head gaskets can leak anywhere; even in multiple locations. Because of that; just checking the compression in the front cylinders is not enough to determine whether the head gaskets are leaking, or if the block is cracked. You really would need to check the compression in ALL the cylinders.
But you could also check the cooling system integrity with a cooling system pressure tester. This is a hand operated pump, and a pressure gauge, which is attached to the radiator filler opening. There are two ways to use it: To check for leaks, you fill the radiator pretty full, attach the tester, and pump the pressure up to about 14 psi; which is the maximum normal operating pressure that will be in the system. On a properly sealed cooling system, the pressure reading should not drop at all for at least 60 seconds. If the pressure does not hold; and there is no visible external leakage, then there probably is a bad head gasket, warped head, and/or cracked head or block. If you find oil in the radiator, and/or coolant in the oil; or the engine starts running very roughly and massive clouds of white smoke pour out the exhaust, you probably have a blown head gasket or cracked head/block.
If the car passes the leak test; the second way to use the pressure tester is to pump up just enough pressure to lift the needle off the peg, and then start the engine when it is cold. If there is a blown head gasket or cracked block; the pressure will rapidly rise to more than 8 psi within about 45 seconds after starting the motor. But if the head gasket and block are intact; the pressure will not rise for at least 3 or 4 minutes (until the coolant heats up to the point where its expansion gradually builds up pressure).
If there are visible leaks on the outside of the engine; a chemical sealer will probably not stop the leaks. But sometimes small internal cracks in the block or head, which do not leak outside the engine, can be sealed by using a sealer specially made for that purpose. The best types are either called Irontite Ceramic motor seal, or K&W Metallic block seal. These types of specialized chemical sealers will not work if there is antifreeze in the cooling system. The antifreeze must first be completely drained and flushed out, and the system filled with tap water. The sealer is then added to the radiator according to the directions, and the engine allowed to idle and run as instructed. The sealer is then left in the cooling system for a specified length of time (usually one or two days). After that, the system must be drained and refilled with antifreeze/water mixture. This doesn't always work; but I once saved a newly rebuilt Pontiac V-8 from being scrapped by this method. It ran for many trouble free years after that.