1987 300SDL Evaporator Leak?
 

My friend's car leaks refrigerant and a mechanic tested it. He said it was leaking from the evaporator. Seeing as that is a bit of a job and someone stole a lot of my tools, I have looked for help online. I saw that some said it could be the expansion valve. Does that also require disassembling the entire dash or is it less work to get to it? Would it just need new rings? Any advice?

The expansion valve is above the accelerator pedal. Not much has to come off to get to it but it's an awkward reach. For the work involved, install a new good quality expansion valve rather than just new seals.

Sixto
98 E320s sedan and wagon

Is it on the left or right side?

The expansion valve is above the accelerator pedal next to the firewall. It is a BEAR to get to. There is a sort of crash "cage" thing in your way to get at some of the fittings, removing the bolts that secure it allow you to move it out of your way. Have some crows-feet ready (17mm, 19mm, 22mm), plenty of swear words at the ready, and be prepared to do some contortions.

The job isn't difficult, it's just the access that's a SERIOUS PAIN! Start to finish, the job should take you about 90 minutes.

Ask the mech, they probably used a sniffer to sample the air from the center vents, in which case I'm highly doubtful that the leak is at the expansion valve.