For cleaning wood chopping blocks, try making up a mix of vinegar, water, dash of eco friendly washing up liquid, squirt of lemon juice and a splash of olive oil. Put it in a squeezy mister bottle like you get in the garden centres. Shake well before each use. You can use it to clean your worktops too. Try neat tung oil wiped on sparingly every now & again, especially after you've given it a clean.. It goes on more easily if its warm - can be mega thick if cold. Or olive oil is not bad for the job. You won't get much oil to soak into oak though, unless its an end grain block, so it will need oiling more regularly than a more permeable wood like sycamore / maple / beech.
Pat