my only concern is about the metal shavings when drilling. It is impossible to prevent everything from falling into the chambers. Also, you often do not have the best position to really be comfortble to drill them out when the head is on the car. Even though it is much more work, I'd rather pull the head and play it safe. Besides, I can replace the valve seals while the head is off, and really clean it out good. There was quite a bit of sludge in there after 150k miles.

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2002 G500 74K
1998 E300 200K and rising
1995 S600 73k


"Some people spend an entire lifetime wondering
if they've made a difference. The Marines don't
have that problem."-Ronald Reagan

"Never tell people how to do things. Tell them
what to do and they will surprise you with their
ingenuity."-General George S. Patton