If you're talking about your air intake boxes, they seal against the filter. If the filter is installed right, there should be no issue.

If you're talking about the manifold plenums, make sure that the bolts are torqued down to spec.... you should be seeing some issues with the engine running if you have a leak here though. Worst case, get a set of NW gaskets and intall them. Easy DIY and cheap....

How did they determine there was a leak??