Are you at least heating the oil to 160degree F? I would be hesitant to ruin a TD engine, finding a replacement will be VERY difficult.

There should already be a rubber plug in the floor pan.

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1995 E420 Schwarz
1995 E300 Weiss
#1987 300D Sturmmachine
#1991 300D Nearly Perfect
#1994 E320 Cabriolet
#1995 E320 Touring
#1985 300D Sedan
OBK #42