I have some problems on my 300E that act like "wounds"...they mysteriously heal themselves over a period of time, instead of suddenly disappearing.
But occasionally, the wound may "re-open"...
2009 ML350 (84K) - Family vehicle
2001 CLK430 Cabriolet (71K) - Wife's car
2005 BMW 645CI (124K) - My daily driver
2012 Mustang V6 (60K) - Daughter's car