Well you need to drain the block and the radiater. If the coolant block drains still has the factory plugs in it your looking at a mess. they usually are very tuff to remove. then you install pet ***** just like found on the radiaters. Its commonly refered to as the Okie Block Drains. A member here some time back made this name up. His signon name was Okiegringo. He lived in Mexico for some time. moved back to the sates finally. Has not been on here is many years. someone here knows him personally too. but anyway once you remove the plugs and drain the block from the cylinder wall drains its not a hard job ro replace the heater. As for leaks with aftermatket heaters. Have not seen any posts like that. Installing them you want to place the probe verticle between the cylinders. don't let it touch the cylinders. Not much more to it really.