PART NO.  SPL.PAGE  DESCRIPTION                                                           
1H3138    15.F.1    Oil seal -(front cover assy, GB assy, 1500, Com GB A8011, none before)
1H3138    16.F.1    Oil seal -(front cover assy, GB assy, 1600 and 1600-MK-II) -changed to
    22H475
1H3138    TC.F.1    Seal -oil -(front cover, gearbox assy, Twin Cam)

Seal Dimensions:
Inside Diameter:  1.062 in (27.0 mm) -- 1-1/16" shaft size
Outside Diameter: 1.756 in (44.5 mm) -- 1-3/4" housing bore
Width:            0.312 in ( 7.9 mm) -- 5/16" seal thickness

    Original MGA part numbers:
BMC		  1H3138  Com.(g)A8011
BMC		  22H475  New part number

    Additional part numbers:
BMC		  88G545
BMC		  OS4498
BMC		  1A3636
BMC		  9204Z90
BMC		  ATJ2034
Moss Motors USA	  120-300
Victoria British  2-2250

Early production MGA did not have a rubber seal at the front of the gearbox. Those gearboxes used a mechanical scroll seal. They can be converted to rubber front seal by installing the later model front cover.

More information about this original type part, and some modern replacement type rubber lip seals, can be found in the gearbox tech article GT-115