Posted 13 January 2012 - 12:27 AM
If it is swivelling it will leak badly and you will have no front brakes. There are several possible reasons why it is swivelling.
Firstly, and what I suspect most, the banjo bolt screws into the top end of the brake hose, which may be rotating in the subframe. There should be a toothed lockwasher under the large nut which fixes it to the subframe. Not sure if they were ever used on the Mini, but some similar hoses used a spring clip instead of the nut and lockwasher, which does tend to allow some movement.
Secondly, the banjo bolt has bottomed in the brake hose because it has been stretched by previous overtightening, or is the wrong bolt,
Thirdly, the copper washers, one each side of the banjo, are missing, so again the bolt bottoms without gripping. You really need new washers, every time, although if the old washers are in very good condition they can be annealed to make them soft again, so they will seal.
Don't overtighten the banjo. They break easily because of the large hole up the middle.