An inline engine is not going to have that problem. Internal vacuum leaks would be on a V engine where the crank case is exposed through the valley. Like an old small block, if you pull the lower the intake, you can see the cam. The lower intake seals that portion of the engine, so if a gasket were to leak on the inside, vacuum would leak into crack case. (Internal vacuum leak) Modern V engines aren't generally designed like that anymore, with the plenum bolting directly to the heads and a sealed valley, so that kind of internal vacuum leak isn't seen very much anymore.
