What is this part? Air conditioning?

[cornblatt]

I feel kind of dumb asking this question, but I have absolutely no knowledge about A/C systems... I tried looking in the service manual I have, but it didn't help me out.

I have discovered some sort of bright yellow oily fluid leaking out of what I suspect to be part of the air conditioning system... see attached photos. This is on a 1984 190D-2.2.

Does anyone know what this part is, and what is leaking out of it? Should it be fixed ASAP, or can I leave it? Should I avoid using the A/C until I get it fixed?