The reverse lights are controlled by the gear recognition switch inside the shifter part no. 210-545-13-32 the cup holder is to blame spilling fluids. On my 98 e320 it was full with coke found one at local salvage yard that worked for $10. Shifter has to come apart to replace.

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1995 E320
1998 E320
1999 E320 4Matic
2000 E320 4Matic
2000 ML320
2007 C230 Sport
2003 Cadillac CTS