Anyone with a Signature have any tips for maintaining/clenaing the leather seats? The Nappa material feels and looks great, though it (understandably) appears to be a bit more delicate than the leather used in the GT and Reserve models. I've had my Sig for about six months and have periodically wiped down the seats with a damp microfiber cloth. I'm starting to get a little creasing on the driver seat by my left leg already. Should I be using any conditioning products? I always hated products that left a shiny or sticky residue, so I've voided using any so far. Thanks!