Remove the 6 10mm screws that hold the plastic pan to the bottom of the engine compartment and you can get right to the back of the alternator. There might be a heat shield or a plastic cover on the back side but you should be able to get at it from the underside with no problems with the drip pan removed.

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Christopher Henkel
1990 190E 2.6 - Arctic white SOLD
1986 190E-16v - Blauswartze
1993 300CE - SOLD
2003 W208 CLK 320 Cabriolet - Magma Red