When rebuilding your VQ37VHR it is nearly impossible to get replacement gaskets for the oil gallery plates on the rear timing chain cover.  Nissan only ever sold these gaskets with the complete cover, so you had to buy an entire new cover assembly.
When one of these two oil gallery gaskets fails and begins to seep, the engine oil pressure may drop resulting in potential catastrophic engine failure.  If you are seeing low oil pressure symptoms, this may be the issue.  And the result of these gaskets failing can lead to accelerated engine baring failure and more damage. 
There are two oil gallery gaskets under the timing cover.  It is always recommended to replace both gaskets.  Recommended torque is 12 ft-lbs.