Mate why not call BW Chiptune in Hayes and get a quote. Speak to Alan there (google them).
Their labour is about 50 an hour rather than 140+ and they charge ECP or better prices for parts, not inflated like BMW.
No harm in asking them right.
ps. copper grease behind the pads, especially the inside pad. I've got the same issue at the mo even though discs/pads are nearly new
It's not always wear related.