If it was a dirty connection, then it's one of two places: the bulb socket or the pigtail. My money is on the pigtail...
I'd recommend putting some "bulb grease" on all the bulb sockets and the pigtail. The grease is available at auto parts stores or Wal-Mart for a few bucks. One tube will last you well into your next two trailers! Clean all the connections with a stiff brush first. Don't forget to put some on the tow vehicle's lights and trailer connector while you're at it.
I'd also recommend opening up the trailer pigtail connector every couple of years to make sure those screw connections are tight. A little grease there wouldn't hurt either.
Glad to hear the installer bought back the Curt time-delay brake controller. You'll be much, much happier (and safer) with the P2.