Are you saying that to zero the gun at 100yds the complete blade is .12" over to the left? It's worth bearing in mind that to zero a Bren, the MPI of the 7 shot single shot group should be 1" to the LEFT of the aiming mark at all distances. So I'd get the zero corrected first and then come back and tell us again.

If it is currently correctly zeroed at 1" to the left and the blades of all barrels is .12" off centre to achieve this then it sort of indicates that it is a gun fault a opposed to a barrel fault. BUT if this was a service gun with an otherwise perfectly serviceable barrel then we say that so long as the edge of the foresight blade is clear of the foresight protector then it is acceptable.

Like Tankie says, don't try faffing about with the body or backsight