Gerald,
Thanks for those points of information. The female connector (that is to twist onto the male pump inlet) appeared to me to have lost any kind of seal. I had a 1/2 ID coned seal and tried that on that connector in situ. It appeared not to be what was designed to be used as the leak persisted due to my not being able to properly seat that cone seal. Now that I've attached the same fitting (on my bench) to the new pump it appears to be tighter and not leaking (but I've not had it under pressure).
Now that I know there is no check valve, that will help in that I won't have to get water spray when I test so thanks for that confirmation. When the weather gets a little warmer in southern Oregon I'll turn off the mains water, drain the line using the valve then disconnect the old pump, take it out, see how it measure up with the new model then hopefully complete the new pump install myself with the fittings I have. I'll try the hardware store or RV supply store in Ashland, OR to see if there is a replacement piece for the one that was leaking even though I did put a cone seal in there.
This fitting appears to seal by having a plastic bulge in the line inside of it, but over time the piece appears to worn to the point that it o longer seals - thus my use of the added cone seal which I still couldn't seal properly when I tried to connect that fitting to the old pump in situ, ie I couldn't tighten it to allow the cone seal to seat. It might also be that the old pump's male inlet union is cracked - I can't see it. With the new pump on my bench it does seem to seal because I can see that the cone seal did move inward as I applied pressure to twist the female connector onto the new pump.
Thanks for the heads up on the cone seal and the lack of check valve.
Mike