He is three years older and has a history of knee and soft tissue injuries. Plus it looks like he may actually stay at Sydney - if he doesn't then he is probably just looking for a final pay day.
I can see why we'd be going after Lumumba - he's not everyone's cup of tea, but he's a good age (27) and has plenty of finals experience.
Even after you mentioned all that I still rather malcheski, he is a star player and worth the risk.