PART NO.  SPL.PAGE  DESCRIPTION                                                           
1H3139    15.F.3    Baffle -oil (behind input ball bearing) -Com.(G)A1861 -Fin.(G)MA8010

Baffle -oil -- for MGA 1500 gearbox -- Com.(G)A1861. Fin.(G)MA8010.
This part was only used for a range of 6250 gearboxes during the production of 1500 model cars. Not used in Twin Cams, and not used in 1600's. Since it was only use in 6.25% of all MGA, I recon it would be a safe bet to remove it and forget about it. The part is (naturally) No Longer Available as a replacement part.

More information about this part can be found in tech article GT-127