It is also important that the gasket be of the proper thickness. Most are not. The two brass horseshoe shims at the ears are .010" thick. The gasket should be the same thickness after it is crushed down as the brass shims. This will allow proper alignment of the transmission input shaft. Most supplier supplied gaskets are way too thin. I make my own gasket from .015" gasket material I get from Napa.
Tom Endy