Re: 85 300D engine mount changeout.%#@! I stripped a hex bolt...
One of the best tools in my box for just this thing is a set of screw extractors. Snap On sells them as does Matco tools and I would guess Mac does too. This tool works real well for removing rounded out alllen head bolts that are deep inside a hole or otherwise hard to get to fastners. Look at the photos I have posted and I think you will see just how well they will work for you. FYI I had this very same problem last week on a 450SL and used these to get the bolt out. Good luck.