Gaskets:
1952-1976 models originally used OEM gasket 25224-52 until 1977 when the 25224-52A came out and replaced the -52 gasket back to 1952.
The -52 gasket has 2 holes in the top center (one for a mounting screw, the other for an oil passage from cover to upper feed galley in the case)
The -52A gasket originally had the same holes as the -52 gasket.

1977-E1981 models were born with gasket 25224-52A.
This gasket went through a modification in L1979 changing the oil feed hole to an elongated slot.
The lower hole in the previous gasket design was elongated upward at an angle to match the case change in that area on L1979 models.
So the original hole location was preserved which allows the revised gasket to be used on previous models.

Gearcase Upper Oil Feed Galley:

• 1957-1981 and some E1982 cases have an elongated angled front to back slot for the oil feed galley in the top of the gearcase.
  A hole is then drilled thru the left end of the slot to feed each rocker box oil line.
  The casting above the oil slot is taller in that area especially on 77-E79 motors.
  Cam Cover gasket was modified (25224-52A) to help control leaks by adding a slot to the oil feed hole.
• L1979 Upper Gearcase Casting Change:
  November of 1979, the MoCo realized a possibile high pressure oil leak around the upper oil seam between the cam cover and the gearcase. ¹⁾
  The case casting was reworked and modified to eliminate this possibility.
  The upper feed galley (slot) profile was changed. The top boss on the gearcase was shaved back.
  The cover gasket also changed to match up to the newer profile.
  The cover gasket (25224-52A) was modified to fit the revised castings and help eliminate possible leaks on earlier crankcases.
• 1982-1985 and some L1981 cases do not have an upper feed oil slot.
  The slot was deleted and the large boss is cast around the feed galley area.
  Oil is fed to the rocker box lines simply by way of a hole drilled thru the large boss in the upper gearcase.
• L1981-E1982 Overlap: L1981-E1982 engines may have one of two different types of gear case cover and crankcase set combinations. ²⁾

1957-E1982 (and some L1981) models use cam cover gasket (25224-52A) 3)	1982-1985 (and some L1981) models use cam cover gasket (25263-81) 4)

Note:
Make sure before using a NOS -52A gasket (on L1979-1981) engines that it has the long slanted slot.

• 1957-E1982 right cases with the small boss and oil slot use gasket (25224-52A).
  57-E79 models can still use gasket 25224-52 with the hole in the upper center and these can be found online.
  L79-81 models must use the 25224-52A gasket with the long slanted slot.
• L1981-1985 right cases with the large boss and horizontal oil hole use gasket (25263-81).
  These models must use gasket 25263-81 with the long horizontal slot.