Two of the o-rings are easily replaceable from the front opening. *The
third o-ring is small (~1/8" ID) and not so easily replaced as it is
deep in the socket. *Wings & Wheels has a nice diagram of the socket
(type UN).

It almost looks to me like you have to dig into the vertical stab and
remove the socket and disassemble it to remove this o-ring, unless
there is a special tool or method to get it out.

Check with Monty Sullivan at M&H in the US. Years ago he described
replacing o-rings in a triple probe on one of M&H's projecgts using a
crochet hook or something similar. He said it was a challenge but he
was able to do it. I don't know if he replaced all three o-rings or
just the easier-to-reach first two.

Chip Bearden
ASW 24 "JB"
USA