Is This C3 A/C Compressor Leaking??

Just to the right of the blue cap (in the center of the photo) & to the left of the ground wire, you can see some of the greenish leak detection dye that has accumulated. The system is curently operational, but I believe that it is only a matter of time until the 134a leaks out.
I think this is just a matter of replacing an "O" ring with a new 134a compatible “O” ring. Note that this is a retro from the original R12 system. I’m suspicious that the current “O” ring was overlooked in the retro process and now needs replacing.
Am I overlooking something, or is this just a matter of taking down the system, replacing the current “O” ring, and recharging it with 134?
Why is there a circlip here in the first place?
What is it holding back?
Before I take it to the "A/C drain and recharge dude", I want to know what I'm getting myself involved with.
Thanks for the help !




