In a large bowl, dissolve yeast in warm water. Add the whole wheat flour, oats, 1 egg, sesame and sunflower seeds, oil, butter, sugar, salt, caraway, vinegar and 2 cups all-purpose flour. Beat until smooth. Add enough remaining flour to form a soft dough.
Turn onto a floured surface; knead until smooth and elastic, about 6-8 minutes. Place in a greased bowl, turning once to grease top. Cover and let rise in warm place until doubled, about 1 hour.
Punch dough down. Shape into 18 round balls; roll each into a 4-1/2 in. circle. Place on grease baking sheets. Beat egg yolk with water; brush over buns. Sprinkle with oats. Cover and let rise until doubled, about 45 minutes.
Bake at 350° for 20 minutes or until golden brown. Remove from pans.