Sound as though you have a leak on the air vac system, the pump is continuing to run to achieve locking /unlocking if you leave the hoses off the pump and block the inlet out let manifold pipes does the pump still continue to run or stop, in other words try and create a test circuit,
my page 41 has a layout of the various connections on the locking system, but it isn't goint to be easy to trace the leak.
http://www.aclassinfo.co.uk/mypage.41.htm
