This is a basic thing but its been a while and I'm doubting my memory based on all of the dumb things I see on the internet.

This weekend I helped a customer replace 45 T's for their call center so they could move some dialers.
In the process they mentioned that the loops they use on their inactive mux ports were touchy, They were all hand made 8p8c with cross connect, probably some were not using plugs rated for solid core wire or with a smaller gauge wire than the plug was rated for which always leads to this kind of touchiness issue.

I was looking online for a seller of molded body, rather than hand made plugs, to end the issue once and for all. But then I noticed that all of the plugs were one of two ways and I can't find a reference that I can trust about which is the correct wiring.

One of the below is not great because it flips polarity the return pair.

Pinout 1: . . . . 1 to 4 and 2 to 5
1 OW/O
2 O/OW
3
4 OW/O
5 O/OW
6
7
8


Pinout 2: . . . . 1 to 5 and 2 to 4
1 OW/O
2 O/OW
3
4 O/OW
5 OW/O
6
7
8

Does anyone know of a good part number to use for something molded and wired correctly?

If they want factory made I just google T1 loopback plug and found a bunch of sites.

Both pinouts you showed are correct, since the circuits are not polarity-sensitive. As long as the transmit pair is looped over to the receive pair, that's all that matters.

What Ed said....

We always made our own 8P8C LB plugs (and purchased the ones for the ADC backfields).Never had a problem.

Sam