Things are progressing nicely at the dealership. They gave a me a free loaner, and took me in the back yesterday to show me the insides of my E300's engine. The Mercedes mechanic said the engine is in surprisingly good condition for a 200k miler, and he doesn't think that anything extra will need to be done besides cleaning the head/intake manifold and all the new gaskets/bolts to put the head back on. All in all, it will cost me about $4k to have the job done, but at least it is done right and I get my diesel back. Lesson learned here: Have patience when you remove glow plugs, and if you're worried at all let the professionals do it.