In the previous thread about MoT test intervals, the subject of brake fluid testing was mentioned. We all know that brake fluid is hygroscopic and that the water can theoretically boil off under extreme conditions, apparently causing 'vapour lock'. I am interested to know if anyone has ever experienced this, or known of a case, with resultant collision or otherwise, which was without doubt caused by vapour lock. I've never heard of a definitely proven actual case of this problem, either in the press or from any other source. All I have seen are several cases of master cylinder failure soon after changing brake fluid , where during the bleeding process, the master cylinder piston has travelled into a corroded part of the cylinder bore, causing seal damage.