A $3 part is very common for A/C failures. I've saved probably 70% of non working A/C systems by replacing core valves. Even when shops have recommended compressor replacements. If a vacuum holds -28 Hg, the leak location is probably a valve core. Some OE designs have only one seal. Replacement cores can have two seals. As a test, use a tool to tighten the cores. If the tool turns even a fraction, the leak location is likely there. If I vacuum a system, I change the cores. I've fully charged systems only to have a core leak. It's good preventative maintenance to change out cores.

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'06 X5 3.0i - bought @143,123 miles (12/26/20)