Uncle Gary's Favorite Streusel Cake

Why I Love This Recipe
Boy how times have changed, Auntie Ranko used to make this all the time, but now Uncle Gary is on a pretty strict diet, so this has kind of become an "heirloom" recipe.
Ingredients You'll Need
2 packages yellow cake mix
1 c sour cream
1/3 c oil
1/4 c sugar
1/4 c water
4 eggs
filling
2 T reserved cake mix
2 T brown sugar
2 1/2 t cinnamon
Glaze
1 C powdered sugar
2 T milk
Directions
combine filling ingredients and set aside
In a large bowl, blend cake mix, sour cream, oil, sugar, water, and eggs
Beat at high speed for 2 minutes
Pour 2/3 of the batter in a greased and floured 10" bundt pan
Sprinkle filling evenly over batter in pan
spread remaining batter over filling
Bake at 375 degrees for 45-55 minutes.
Cool for 25 minutes then remove from pan
blend powdered sugar and milk together, drizzle over cake