345D oil pan leaks

Working on a 345D RAJ s/n prefix, C13 engine MHX prefix.  We have resealed the oil pans on several of these machines multiple times, usually after 800 to 1,000 hrs run time.  New Cat isolation seal & fastener assemblies.  The bolts are torqued to spec and are still tight when the pans start leaking again.  Any suggestions would be appreciated.