Hi Courtney-
Welcome to the forum. You don't say in your profile where you are- and it might help if someone can tell where you are so they can recommend a shop for you.

For me, I did my own GPs in the 190d, but after reading a number of "broken glow plug" posts on e300s- I decided to take it to my indie which also has a machine shop. I brought him new cans of PB Blaster, Deep Creep, and WD40, 6 glow plugs and a new tube of anti-sieze compound. When I dropped it off, I begged them to drench the GPs asap while the motor was still warm. He told me not to worry. I worried anyway- but was relieved when they called to let me know it was "no problem" and the car was ready. That was until I had to paid him $600 for this simple job. Was it worth it? I doubt it-and I'm sure I would have had to pay more if they had broken one anyway. Oh well- maybe I'm wrong and maybe it was better that they did the work.

I think one good piece of advice that I received from one of the gurus on this board bears repeating- replace the glow plugs before they fail- because the longer they are in there- the more likely they are to become seized due to heat and cooling cycles, the build up of soot, and etc. I replaced mine at 140K and it starts perfectly and very quickly now. Maybe replacing them at 140K saved me a cylinder head repair at 200K.?