The aircraft had a rudder/directional control problem that had been occurring intermittently. When it occurred during the previous flight, the pilot had to use full right rudder to keep the ball centered. Before landing on that flight, he made a low pass near the tower. Tower personnel advised that the nose gear appeared to be cocked to the left. While landing after that flight, directional control was difficult. After inspecting the plane, a mechanic advised that the nose gear appeared to have too much oil and not enough air, causing the gear oleo to not fully extend. The pilot elected to return to Spokane before having it repaired. After takeoff, the problem recurred, but required full left rudder. Later, oil was noted coming from behind the control panel. Not knowing from where or how bad the leak was, he diverted to the nearest airport and landed with a 10 knot tailwind. When the nosewheel touched down, the plane veered right and hit a snowbank. The runway was too slippery for the left brake to help.