My 2009 Exclusive Tourer has developed an intermittent tendency to sink at the back end when parked over the last week. Seem to recall mention of an anti sink valve and or sphere? There do not appear to be any fluid leaks and if I restart the engine and adjust the suspension level to high and back to normal it seems to stay up. Question is, shall I just put up with this or is it something which could have further consequences so should be fixed? If so, any ideas how much it might cost to rectify? Pleased to hear.