You want to use an oil, so it will soak into the pores of the wood and keep if from drying out, warping and splitting. If the board is in an environment that is normal to high humidity (i.e. NOT in a North American hot-air heated house in the winter), then it may not be a problem, which could be the case locally for you, don't know. Good habits also help, as in wiping down the board immediately, so it does not have water/fluids sitting on it. I don't think Vaseline is a good option, because it is a solid at room temperature. So, it will just sit on the surface and not really soak in. I suppose you could rub it in really well (maybe with a hot towel?), but my guess is that there would be some kind of greasy residue. Do they sell linseed/flaxseed oil locally as a dietary supplement? Can also be used and not as likely to go rancid as vegetable oil. If you can get medical grade mineral oil, get it and use it. It has very high purity. In reality, since mineral oil is a commodity item, it is probably the same cut as the food grade. But, medical grade is U.S.P. tested for purity and quality.