Don't recall if Montour Trail is under County Parks jurisdiction, but if so you might be able to report it via the County contact form at http://www.county.allegheny.pa.us/feedback/index.asp or call the County Parks Department at (412) 350-7275.
If I'm not mistaken, the ramp from 51 to the Montour Trailhead is in Moon Twp. Their 311-like system (the "Citizen Request System") is here: http://www.egovlink.com/moontwp/action.asp