I have two exhaust manifolds for sale Right, 1383648 date 259 Left, 1238899 date 252 $250 for set plus shipping. In the interest of full disclosure, the right manifold has a couple of points. The bolt hole between #4 and #6 has a hole in the casting. The hole cannot be seen, unless the bolt is removed. Exhaust gases would want to escape from the bolt head. Sealant and or a sleeve would correct. I am sure this hole, in the casting, has been there since 1970. I have inquired with a long time Buick guy, and he has never experienced this. The inner bolt hole has been slightly enlarged, during the bolt extraction. More can be seen in attached pics.
