Yesterday I fully flushed my 1999 E300 OM606 and was hoping to replace my thermostat in the process with 6022000015 thermostat and 6032030474 thermostat housing after filling with fluid housing began leaking profusely. Is there something I need to know about installing the O-ring seal beforehand? I even took it apart and used a different O-ring after and still same issue. Thanks