my benz has clocked just over 260,000 miles and one of the glow plugs went out. On top of that it got really cold so i've had rough cold starts for about a a week and a half. i had sourced a set of oe replacement glow plugs from carquest they are bosch brand and look identical to factory , and tried replacing them yesterday . Cylinder 2 plug was the one that was out via the resistance check at the relay and was the one that broke off but i replaced all of them anyway . So back to the broken plug i was slowly working it back and forth trying to get it out and it snapped , i barely had 1 thread out . so i moved one to the next one in line Cylinder 3 and 6 were tough also but did not break , i used a lot of penetrating oil (lps kb88 penetrating oil) cylinders 1, 4, 5 came out super easy i just broke them loose and they screwed out by fingers . But anyways the point of my post is that if you brake a glow plug in the head while trying to replace it don't freak out like i did and order a head gasket kit .The head does not need to come off . you may meed to remove the oil filter housing if you break number 6 glow plug to have better access to it. but since i broke number 2 i just had to remove the fuel lines for cylinder 3,4,5,6 . i ended up braking the electrode off to remove the hex portion of the plug then i borke the rest of it off flush with the head of the engine and had to drill the electrode about an inch further down into the head , make sure you use good drill bits and not too big you want to save the threads in the head . then we tried a matco brand extractor which ended up braking but fortunately didn't get stuck then i borrowed a couple of different design extractors from a friend the erwing brand reverse thread didnt work so i used the square wedge type (unfortunately i don't know what brand they were) and it got the threaded portion out it was slow and it broke into 4 pieces plus there was still the rest of the plug stuck in the head held by carbon . we drilled the electrode some more and tried threading it and using a slide hammer to get it out which didnt work and when in came loose it broke the plastic supply fitting off of the primer pump which should tell you why there is a diesel puddle under the car in my picture . so then we drilled the electrode a bit deeper and hammered a smaller square wedge type extractor in it and with use of penetrating oil worked it back and forth until it was spinning more freely and the rest of the plug cam out . now i have six new glow plugs installed waiting on a new primer pump should have it tomorrow and have the car running again. Just wanted to post this for the DIY guys and let them know that its worth trying everything you can think of before pulling the head .