I had a local shop use a generic sniffer to verify that refrigerant was being lost through the evaporator in my '95 320.
Then I changed it out a few months ago. I re-did all the foam seals while it was apart. It's not a hard task; it is an extensive one.

What foam seals?

There is a door or 2 in the heat/AC suitcase that is sealed with foam plastic/rubber. As is the heater core and evapaorator. It was all very brittle. As was the seal fo the suitcase to the firewall. I bought new adhesive backed foam at the hardware store.

Note taken! Thanks.