Just had number 4 replaced at local MB dealer ,after I brought my 3.0 cdi viano in Nov 2013, apparently its the one that goes before all the others. Had to leave with them for 2days as they were 'easing' it out and didn't want to snap it off. Had the relay replaced at the same time as it had fried it. Got to have number 5 replaced at a later date as that's gone also. MB dealer did advise that it might have problems starting if weather got really cold but no issues so far ,just glow plug light stays on for 30seconds or so after you start, but fine otherwise