I suggest using mineral oil (I just put some on my block today) and periodically putting on a half-and-half mixture of mineral oil and paraffin wax. You will have to heat the mineral oil and wax to get the wax to melt. Apply it with a rag and rub it into the block. Let it dry overnight and scrape off the excess with a flat spatula. (I put newspaper under the block to catch all the scrapings.) Then rub in what's left on the block.
I melt the wax and mineral oil and wax in old (dry inside) can on the stove on low. Be very careful and don't look away when you do this, as it is very flammable. After I'm finished I cover the can and put the leftover oil/wax in the fridge until the next time I need it.
I used olive oil in the past and it did become rancid. (Sorry Steve, but that was my experience. Maybe I did something different from you.) It took a long time to get the block clean. It makes sense when you think about it, as all cooking oils including olive oil do oxidize when exposed to air.
Or, use what the manufacturers use. Check out: http://www.johnboos.com
Good luck and enjoy your block! Happy Easter everyone.