I'm lazy, I use Nikwax Water Based Wax. Can apply it when the leather is wet (it actually works better that way, penetrates more and slows drying to reduce cracking). It's easy to apply. And it doesn't soften leather at all, so you can keep applying it. I just keep slathering it on, it only soaks in where the leather is not water proof, leave it for a bit and wipe off the excess. Eventually you reach the stage where the leather is impregnated pretty well and your seat won't get wet in anything other than a flood or a monsoon. Really good for leather boots too, not animal based, so won't cause mould or rot. https://www.nikwax.com/en-gb/product...d=74&activity=