I'm pretty sure once your breather is "breathing", you won't have seal issues. The O rings on the ARB's do need servicing occasionally, but I bet that too will be better
Not sure how M-C would know they would end up here, VISA billing I suppose, or verified PayPal. I've not dealt with M-C, but I always assumed I'd have no trouble shipping to a US address
I'm in Blaine, WA quite often (like every three or four days). I'm doing the same thing for a buddy on Vancouver Island, I have an address that you can ship stuff to, then I just drive across and bring them home. CBSA has no issue as long as I'm under $200 of declared value. Border waits aren't...