When I replied earlier, I didn't know you were out in Bolivia. My remarks were aimed at someone working at home with the usual tools and facilities. In your circumstances, I would be tempted to leave it alone and get it to mechanic or BMW dealer when you can. Just ride around the problem for now.
Given that this is not just a simple case of bleeding the rear line and caliper (thank you BMW), I would sooner do that than risk losing the brake completely.
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