Yes, MU still fly to SEA, I don't know how often though. Most flights arrive from ANC, and continue to JFK. I do not think they stop over on the return. Also, Atlas Air operates these flights sometimes, more so lately.
727, L1011, MD80, A300, 777-200, 737-300, 737-700, 747-400, 757-200, 737-800, A320. E190, E135, 767-200, CRJ9