Wow! How old were those spark plugs? The ceramic burn through was really bad. Those are some of worst I've seen.

What is the MAF reading when it's plugged in? Reading in grams/sec. It should be close to engine size at operating temperature. The sensor could be bad. Is it an OEM old one? If it's very old, replace it or borrow one to try out. The orange glue looks like sensor "coating". I have not look at one closely but it should be normal unless it looks burned.

When everything is working properly, front O2 sensor voltages should cycle up and down. The rear O2 sensor should read steady voltage. The rear voltage will change with idle RPMs but stay mostly flat at constant RPM. If rear O2 voltages mimics front O2 cycling, there's a problem.

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