PART NO.  SPL.PAGE  DESCRIPTION                                                           
1H3084    15.F.1    Extension -gearbox -Changed to 1H3149 Com.(G)A101 -
    Changed to 1H3273 Com.(E)GD101
1H3149    15.F.1    Extension -gearbox -Com.(G)A101 -(was 1H3084) -
    Changed to 1H3273 Com.(E)GD101
1H3273    15.F.1    Extension -gearbox -Com.(E)GD101 -(was 1H3149)
1H3273     16.F.1    Extension -rear -(gearbox assy, 1600 and 1600-MK-II)
1H3273     TC.F.1    Extension -gearbox -(gearbox assembly, Twin Cam)
1G3418   15.F.1     20  Bush (gearbox rear, early and mid 1500) -Fin.(E)GB51767
6K529     15.F.1    24 Bearing -rear extension(gearbox) -Com.(E)GD101 (high starter 1500 on)
6K529     16.F.1    24 Bearing -rear extension -(gearbox assy, 1600 and 1600-MK-II)
6K529     TC.F.1    24 Bearing -rear extension -(gearbox assembly, Twin Cam)
11G3147   15.F.1    21 Oil seal assy (early 1500 gearbox) -Changed to 1H3339 Com.(G)A101
1H3339    15.F.1    22 Oil seal (internal mid 1500 gearbox) Com.(G)A101 (mid 1500)-
    (Prev 11G3147 external) -changed again to 1H3275 Com.(E)GD101 (late 1500)
1H3275    15.F.1    23 Oil seal (internal late 1500 gearbox)  Com.(E)GD101 (late 1500)
    -(previously 1H3339)
1H3275    TC.F.1    23 Seal  Oil seal -(rear extension, gearbox assembly, Twin Cam)
1H3275    16.F.1    23 Oil seal -rear extension -(internal, gearbox assy, 1600 and
    1600-MK-II)
CCN240    15.F.1    25 Circlip -oil seal -(gearbox rear, GB assy, late 1500)
CCN240    16.F.1    25 Circlip -oil seal -(gearbox rear, GB assy, 1600 & 1600-MK-II)
CCN240    TC.F.1    25 Circlip -oil seal -(rear extension, gearbox assembly, Twin Cam)
1H3304    15.F.3    26 Flange -3rd motion shaft -Com.(G)GD101 (gearbox, late 1500)
1H3304    16.F.2    26 Flange -3rd motion shaft -(gearbox, 1600 and 1600-MK-II)
1H3304    TC.F.3    26 Flange -3rd motion shaft -(gearbox, Twin Cam)
LWZ212    15.F.3    27 Lock washer (rear flange) -Com.(G)GD101 -(Prev. locktab 11G3226)
LWZ212    16.F.2    27 Washer -spring -nut -(3rd motion shaft flange, gearbox, 1600 and
    1600-MK-II)
LWZ212    TC.F.3    27 Washer for nut (spring) -(flange, 3rd motion shaft, gearbox, Twin Cam)
FNZ612    15.H.2    28 Nut for flange (differential input, 1500)
FNZ612    16.F.2    28  Nut -3rd motion shaft flange -(gearbox, 1600 and 1600-MK-II)91240
FNZ612    TC.F.3    28 Nut for flange -(3rd motion shaft, gearbox, Twin Cam)

Item 25 - CCN240 Circlip is a large internal snap ring to be used in the rear extension for all of the MGA (and early MGB) high starter gearboxes, including all Twin Cam1958-1960, MGA 1500 Com.(E)GD101 in Jan 1959, all 1600 and 1600-MK-II, and all 1600 "Deluxe" and 1600-MK-II "Deluxe" 1960-1962, and MGB 3-synchronizer gearbox through 1967.

Material: Phosphate coated carbon steel For ID: 2-1/2" Dia: 2.648" Width: 0.086" OD: 2.775" Thickness: 0.078"

McMaster-Carr: 5449A93 (pkg of 5) Internal Retaining Ring Hardness: RC40 Thrust capacity: 28,000-lb Spec's met: ASME B18.27.1

Note: Not sure if the stated thickness of 0.078" is same as the original BC part, but as long as the housing internal groove is wider than the ring thickness, this replacement part should work.

While BMC called this "Circlip -oil seal", it does not need to touch the oil seal. It actually serves as a physical stop for the ball bearing while the extension housing is being installed over the third motion shaft.

The bearing has Locational Clearance Fit (very close slip fit) with both the housing and the shaft. The bearing is installed in the housing first, followed by the retaining ring. As the housing is being installed over the shaft to abut against the main case, the retaining ring prevents the bearing from being pushed out of the housing, possibly dislodging the seal (if the seal was already installed). After everything is assembled and bolted up securely, the bearing is captured tightly on the shaft and can float axially in the housing. In operation the bearing does not mate with any shoulder in the housing, and does not touch the retaining ring. The rear seal should be installed flush with tail end of the housing, and does not touch the retaining ring.