I can agree that ABS are unacceptable on all levels and that H4D is the best camera.
However, there's absolutely no problem with a US dealer.
Remember you are working for an organization and playing with other people's money.
When it's your own money you will mind very much if the dealer gouges you unfairly.
Jugend don't have any high end backs on hand - they get them from Leaf when needed.
I've bought three backs in the past six years, one from Jugend and two from abroad.
The only one that gave me major problems and serious expenditure is the one Jugend sold me.
Maybe if I was an institution like your employer, and not just a private photographer, they would pay better mind to treating me right, but they sure didn't.
In any case I've had no problems whatsoever getting service from Leaf regardless of where I got the back.
The malfunctions you are describing are body not back - a totally different thing - Mamiya bodies and lenses are handled by Shimoni and sent to Japan for major repairs.
You can get spare bodies for $2-3K and still your expenditure is way less than what Jugend charges.