I may be way off the mark but I had a similar problem on S1 and ended up as a leaking pipe on the steering pump, with the oil tracking across the underneath to the other side of the car! Not sure if the S4 has the same problem?

15 Weissman GT5
11 Aero8 SS
21 Q7
23 RR
24 Def'r 130
1960 XK150 DHC
1970 E-type
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