There is a great discussion in an entry and comments in …jurabilis! on the two forms Schadenersatz and Schadensersatz. I remember puzzling about this for many years when I was teaching legal translation. We used to discuss translations into German, even if I didn’t teach them myself.
We eventually decided to use Schadensersatz all the time, but had the feeling that German lawyers preferred it without the S in the middle – there were always a public prosecutor and a judge doing some of the teaching.
The BGB has SchadenSersatz too, but was that always the case? Apparently so. The form without the S is used in Austria – surprisingly, when one considers words like Erbseinsetzung and Erbserklärung, which always remind me of Erbsensuppe.
This has even been discussed by Bastian Sick, but to little effect, as usual.