Here is my experience with drilling a plug out - http://www.peachparts.com/shopforum/showthread.php?t=109101&highlight=glow+plug

Haven't heard from the original poster in a month, so I'm assuming he figured things out. I haven't checked this forum for a long time and I'm likely too late, but I do have the proper reamer and tap and a few other things needed or helpful for removing glow plugs on the E300's.

__________________
Len
'59 220S Cabriolet-SOLD and living happily in Malta
'83 240D 351,500 miles original owner-SOLD
'88 560SL 41,000 miles - totaled and parted out
https://sites.google.com/site/mercedesstuff/home
'99 E300 turbo 227,500 miles
'03 SLK320 40,000 miles - gave to my daughter
'14 Smart electric coupe 28,500 miles
'14 Smart electric cabriolet 28,500 miles
'15 Smart electric coupe 28,000 miles