I am wondering whether LIEBRUCKS can be derived like this:
Lithuanian LIURBAS (which provided the widespread East-Prussian LORBAS = "cheeky young boy") plus ending UKAS. R and B change places, since LIBRUKAS is pronounced more easily than LIURBUKAS.
hard to say
if you interested you can check anytime any word root in Dictionary of the Lithuanian Language online at http://www.lkz.lt/startas.htm