Hi.I'm pleased that you have managed to cure the rattle.Like me,you must have thought at some stage that a new / reconditioned gearbox was required.This rattle must be one of the most common - annoying things to happen to an mg,when a few miles appear on the clock.
Hopefully this information will help a lot of people with an mgb as there is no other information on this in any manuals.
What a great site this is.
Phil
phil wilkins