I'm guessing they've said "Well mate if it's a chain it's £1.6k, but then if the engine has gone, and it's a 4x4 (assuming it's an xDrive), then the subframe has to come off, and yada yada yada.) Not sure exactly how they'd excuse it. Even if it is the engine, he's looking at £3k max for a recon. Not even BMW would charge what he's been quoted.