Since you've got that resident claiming it's slippery when wet, I say go after the local hwy department to cover your damage. Especially if there's no "slippery when wet" caution sign, it could make for a big negligence suit if you cared to pursue it.
I've never been a fan of suing for stuff like this, but when you can go after gov't, I'm all for it. :)
'12 Suzuki V-Strom DL650
'96 Suzuki DR650
'92 Yamaha TW200