export/import BOM and lost expressions

[Mike686]

Hi, i have trouble with the BOM

basicly i've set a BOM for parts only with the folowing columns

Item, Part Number, Item QTY ,Stock Number, description and cost center (i use this one to indicate Vertical and horizontal)

i've made and expresion for the part number so that it equal (stock number X G_L - Cost center)

everything work fine but i want to use this in other assembly, new or old

i've try the export command, the import it in another assembly but the expression don't follow

is it because the part in the fiorst place dont a a value for the cost center than it dont work?

how should i proceed to make this work