It was reported in a US newspaper (can’t remember which one) a few days ago that the Russians have said the trains were probably used to dispose of the bodies of concentration camp and/or slave labourers from nearby camps. As the Russians were first into that area in 1945 they might well know something about it. And if you think about it, the claim makes sense after the efforts the Nazis went to in order to destroy evidence of their atrocities. So maybe no aviation content (or gold) at all.