In small bowl, combine mayonnaise, chili sauce and horseradish; mix well. Spread each slice of bread with butter. Place bread, buttered side down on cutting board. Place a slice of cheese on all slices of bread (unbuttered side). Divide corned beef and place on top of cheese on four slices. Top with mayonnaise mixture and sauerkraut.
Close sandwiches with remaining bread - cheese side down, butter side up. (Each sandwich should have the buttered side of bread facing outwards.)
Cook on a preheated large griddle (or cook two sandwiches at a time in a large skillet) over medium-low heat 4 to 5 minutes per side or until bread is toasted and cheese is melted.