Niagra Falls kind of a leak

Now I need answers. Badly. Not to be rude but im all out of ideas at this point. My first question on here was whether I should replace the pipe or the engine. Got an answer. So I replaced the pipe. That didnt work. Turns out that the threads that the pipe screws into on the intake are all gone. It is completely smooth except for the very back where I believe there are three threads left. I put a thread sealer on the pipe and screwed it back in as far as it will go. Tested it out today and found out that the leak is much worse than before. What did I do wrong and what do I do to fix it? I'm at the end of my rope here so I desperately need answers. Please.