Actually…. Leather is not easy to maintain if you let it get into contact with bodily fluids. The best you can do, without damaging leather is to wipe it clean with hydrogen peroxide right after use. That would apply to a harness of course. If you have dildo made out of leather you will be safe only by using condoms on it (use non-lubricated and double it up just in case). Leather will absorb the moisture and/or any bodily fluids much better than latex or plastic.

do a Google on sex toys maintenance: Handle With Care