Richard the diff fluid is self contained in the diff. The diff has a gasket on the rear plate and a seal on each of the input and output shafts.
The shock absorbers also have their own self contained fluid.
Maybe what you are looking at is the self levelling system. From memory this was introduced on the 411 S3. That often leaks and isn't really much use. There's a reservoir and pump for this in the engine bay, which you can safely remove.
Can you post a picture of the offending leak?
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