If in doubt, use the Wilson's Leather & Suede Protector. It does not change the color, shine, or texture of the leather, and I have used it on all my LP bags.
Good luck, and I hope that spot lightens up for you.
I thought I read on tPF someplace that LP bags needed no conditioning - something about them being specially dyed in some kind of enzyme-treatment or something. I can't find it now. But - I've got two Speedys coming, and am thinking about buying a berry Danielle shoulder bag, so this is good to know - I've got Wilson's.
ugh, i should have just gone with the spray only! i just got so paranoid with my bag. hopefully if i let it dry a few days, itll lighten up? i read somewhere that another person had their bag darkened a few days after treating it. i didnt konw itd last that long!