I had a fitting crack and start leaking on my Mytee 1003DX. I was able to get it off no problem but can't figure out how to get the new fitting back on without kinking the black hose. Here's a couple pics that I hope explain what I'm trying to say:
Your last pic like Ed said looks to swivel. And looks like theres a 90 connected already. Youll need to unthread that 90 from hose. Put your new piece and 90 together without hose. Thread those pieces as a whole into where ever they came from lol. Hose is last. Sometimes once tightened the swivel will lock up. So it goes on last. Like mentioned teflon the threads. Or use thread sealant.
Better over all pic with ends and where it goes would help us help you more better.