I think the expansion valve on this setup as it sounds just like the way my 300d is set up is a little square looking thing under the dash by the evaporator. Since the system blew open I would change it out as well cause they have tiny holes and will plug up, rust, etc.
I guess I got lucky with my 77 240d with the York compressor, what an easy thing to R&R if needed

Also that 10k fine think sounds like BS to me. A shop doing it yes, your neighbor claiming you did it? Prove it. My system was M-T before I started the work. Show me the gas I let loose