The problem is the return trip home, the export. The gunsmith must be FFL'd for Export or you, mostly him, will be in trouble for the shipment back to you. The cost for permits may exceed the cost of the work done or a new part. Often it is better to buy the new piece than ship yours south. If you must, it may be better if you did a temporary import in person with the appropriate ATF forms approved in-hand, and you stayed in the USA to re-export it back to Canada when the work is completed.
