Heater inlet pipe keep commander 5.7 sealing issue

I put a new water pump in the command and the old ring was split so it looked like a 5/8 x1/2 but leaked ...got the Mopar o ring at $13 and it leaks . I'm not sure if it's the tube or the bore on the new water pump that has the issue so I'm.not certain a complete inlet tube assembly will fix the issue as it might be the pump bore...lol...and to access the tube to remove and replace requires extra work of removing the intake so I'd like to skip that of I can. I've applied a liberal amount of black rtv to pipe and it will sit unt I jet back from Albuquerque if that doesn't seal it I'm looking at trying the next size up OD o-ring at 11/16 x1/2 . I did put a larger o ring at the lip on the inlet pipe it did stop the leak until it ripped so that's why Im giving the rtv a try and I had it sitting in my tool box and could do it between runs while at the yard... Lol... any suggestions besides tapping the pump for npt threads . I'm just suspicious that the pump bore is the issue and the time spent on replacement of the pipe will still yield a leaking heater inlet after all is done