I've got some harness boots which I've had for a few years. I wear them a few times a month and don't do much for them in terms of specific care or maintenance. The other day I was wearing them, and a road-grimey auto part tipped over and landed on my toe. My foot's fine (thanks boots!) but they sustained a big black smear. Any tips on getting this off? The boots are oiled leather, so it's not a super fine finish. Here are the boots, mine have black soles, FWIW. and the stain: Also, can you suggest general care and maintenance for the boots? Should I condition them periodically? Thanks.