Hafler 9130 Right Input RCA loose... How do I access this?

You probably have to pull up the main PCB, screwed down.
Trouble could ensue. If holding the jack flush mitigates the ’open’ maybe you could glue it.
It kinda depends if it’s grounded (return) to case. If it’s not apparent uou could check with a meter. If it's grounded just use spots ofj glue or JB Weld one side.
Best of luck.

Look at the PC board, directly above the RCAs (either side of the stereo/mono switch, behind/under the two, yellow, metalized Mylar caps).    Examine the solder through-holes (solder points) for the RCAs (there should be three each) and look for cracks, in the board.      If everything still looks secure, the jack itself may be broken.    If not: re-solder, or repair the board, as necessary (ie: solder/jumper the trace and Superglue or epoxy any crack).       If the RCA needs replacement: the board has to come loose.  That will require detaching the output transistors from the heat sinks, a few mount screws and unplugging that connector between the power supply caps.     Remember to refresh the heat sink compound, during reassembly.   I've replaced the RCAs in a few Haflers and other manufacturers' equipment, with these:  (https://www.wbt.de/english/products/a/Detailansicht/Artikel/topline-cinchbuchse-3.html), though: I can't swear they will fit the 9130.

Thank you both for your quick and informative replies. I wasn't able to get to it until today and it looks like I (hopefully) had it all wrong. The jack itself doesn't seem to move much. I think the RCA jacks are just slightly smaller than those on other devices (worn?) and my interconnect was slightly large so I compressed the ring a skosh and all seems well. The cable fits snugly enough on new devices but was sloppy on the Hafler. Fingers crossed.

Thanks again for your time.
Mike.