Eventually I'll write down the entire proccess, but the basics to keeping and maintaining any kind of leather starts with this (from my own experience):
Polish with a good quality leather conditioner once in a while (horseman's own is my favorite)
Use black saddle soap inbetween conditionings (you do not want to condition very often, it can often make the leather greasy)
for brass/silver, nevrdull is wonderful. first use the nevrdull, then clean with YELLOW saddle soap. this removes the excess polish from the metal and leather around it (will look white when dry, you don't want that)
If the harness begins molding - Vinegar. seriously. It keeps the mold at bay longer, while doing no harm to the leather. You don't want to do this too often however. Just when you see mold begin to grow. If the problem persists, and if you live in a humid area - invest in a dehumidifier. It helps take away a lot of the mold and mildew before it has the chance to grow.
Green 'gunk' on brass - gently scrape off with screwdriver (flathead, smallest one you can find) and then polish with the neverdull and yellow saddle soap.
When exposed to sweat - every time the harness comes off you should rub it down with a rag while it's still warm. leaving the sweat and hair on it to dry can dry out the harness and make it harder to clean. Use neatsfoot oil (sparingly) if the leather begins to look dry and brittle, it works also as a conditioner. but like i said, only use sparingly, too much too often can disolve the stitching. DO NOT PUT ON PATENT LEATHER! it will peel it.
hope this is helpful!
