I would say to take the servo casing apart and get some compressed air in there to dry it out. Try spraying WD-40 in it to displace the water. Before putting it back together, run a small bead of silicone along the casing where the 2 halves meet. You may also want to put them in balloons just in case! When you put it back in the care, double check the rx as well. Make sure it's dry and plug everything in and hope for the best. Run the throttle and steering servos to see if they are reacting to your input.
As far as the tires, I am assuming it's rubber. You "can" wash them. Just make sure that you let them dry well. Water might get into the vent holes inside the rim and wet the foams on the inside. If they are wet, it will cause an imbalance and make the tire wobble. Just to make sure, when you clean the tires, cover the hole with some electricle tape or just make sure it's covered. Don't squeeze the tire under runing water or it will suck in the water.