The oil? Best free flux in the world! The clips? No problem at all!
The worst of it nowadays is that many of the zinc clips are not marked as zinc. If even one gets into your lead, good luck with your casting!
You have to be extremely diligent to test each WW for softness so you don't let a zinc one slip past. I scratch mine on the pavement. The zinc is harder. A real problem and PITA.