I read the cover on the LPOP wears , causing drain back.. Also ....Read this.....
A deareation valve was inserted in the front cover beginning with engine serial number 201681 through engine serial number 375549.
The front cover was redesigned starting with engine serial number 375549 to help keep the oil pump primed for initial start up.
To accommodate this change, the pump inlet port was rotated 90° which moved the pickup tube from the left to the right.
The front oil cooler header gasket was also redesigned because of the change to the front cover.
The front cover has been modified for the updated reservoir to front cover gasket and passages have been cast and drilled into the front cover to incorporate the standpipe.
The engine serial number that the standpipe was incorporated is 201681
The high pressure pump has had the drain check valve deleted. This brings the variation of high pressure pumps used on the DIT to three. The pumps may be identified by the absence or presence of the anti-drain check valve.
On 1994 1/2 and 1995 model year engines up to serial number 187099, the initial high pressure pump did have a drain check valve but did not have an edge filter. The edge filter was part of the injection pressure regulator.
On 1995 model year engines starting with serial number 187100, up to serial number 201680, the high pressure pump did have a drain check valve and an integral edge filter. The edge filter was deleted from the injection pressure regulator.
On 1996 model year engines starting with serial number 201681, the high pressure pump does not have a drain check valve but continues to have an integral edge filter.
High Pressure Pump Gasket
The high pressure pump gasket has been modified to seal the standpipe between the pump and front cover.
Note: The correct gasket must be used to prevent internal and external oil leaks.
Injection Pressure Regulator (IPR)
On all engines starting with engine serial number 187100 and above, the injection pressure regulator does not have an edge filter, but the high pressure pump does.
Note: There is now a service package for the IPR o-rings that allow you to replace them separately if needed.