With the EGR tube on my '98 gone, I can have the plugs accessible and changed in about 30 minutes. Since it's that easy, I have never bothered replacing all of them at once.

When I bought the car, I pulled and checked all of the plugs and then applied silver anti-sieze and reinstalled them with the proper torque. Since then, I have never had a problem replacing them as they go out.

Call me crazy but I just use whatever brand of GP I can find. I have used Bosch, Beru, Autolite and NGK without problems.

Here's a cross reference I found on line of all of the OM606 GP model numbers from manufacturer's around the world:

ACDelco 118G
BERU 0100226210
BERU 0100226235
BERU 0100226457
BERU 948MJ
BERU GN948
BOSCH 0250201038
BOSCH 0250201048C
CHAMPION CH177
DELPHI HDS354
DENSO DG-106
GENERALMOTORS 88900727
HKT B-082
HKT B-099
MARELLI UX17A
MERCEDES 11592001
MERCEDES 11592101
MERCEDES 1592101
NGK DP16
NGK Y-925J
NGK Y-925R
OPEL 88900727
PSA 596035

__________________
-Evan


Benz Fleet:
1968 UNIMOG 404.114
1998 E300
2008 E63


Non-Benz Fleet:
1992 Aerostar
1993 MR2
2000 F250