Further evidence from the FDR should answer a few questions regarding the behavior of the braking, spoiler and T/R systems. I say should because I'm not sure that wheel speed and anti-skid valve parameters are monitored by the FDR on an '80s vintage MD-80. Anyone know? If not, then maybe the installed QAR does?
Good point made by bubbers regarding the loss of rudder effectiveness caused by reverse thrust "blanking" which occurs on many tail pylon mounted engine equipped airplanes. Have noted that on all such types I've flown. A left crosswind component of 7 knots doesn't seem like very much, but the "parachute effect" of T/Rs dragging the tail downwind (to the right) and the loss of rudder effectiveness (promoting a weather-vane tendency) combined might create a noticeable left turning tendency. On a slick runway, these factors have contributed to MD-80 landing roll-out directional control difficulties in the past. Good FDR or QAR data may answer those questions.
That must be a horrible feeling when you realize you're going off the runway in spite of all your efforts to prevent it. Anyone who's landed on a slippery runway has probably had their moments of doubt, but actually going off? I sure don't wanna know. Glad it didn't turn out as bad as it could have.