So they aren't demanding serial numbers to buy repair parts? I wouldn't
expect nor would I even try to get warranty -service- on any grey market
item. IMHO that goes with the territory: same money, take some risk.

This is not true, though Mamiya would like you to think it is.

Also not true.

You are allowed to bring in ONE item of each kind (ie, one body, one 80 mm
lens, etc) legally once a month.  You cannot bring in more than one of any
given item within that time frame though.

When I bought a Mamiya lens grey market it was indeed inspected by customs and
I had to pay duty (I think 4% or so) but it was certainly legal.

http://medfmt.8k.com/mf/hongkong.html and scroll down to the part on trademarks
(BobM used to do good work before he morphed into the digital anti-Christ :).  
To quote from Bob's page on this issue, specifically Mamiya ...

<quote>In the past, Mamiya America Corp. has protected their valuable
trademarks and associated rights to control the importation and distribution of
these Mamiya trademarked photo items (cameras such as Mamiya 7 RF, RZ-67, and
Mamiya lenses). We are not talking about bogus badly made copies of Mamiya
products. These items were actually made by the Mamiya Japan entity at its
Japanese and other foreign factories to full specifications.

Bringing in a single one of each restricted trademarked item is permitted for
personal use under U.S. laws. But bringing in multiples of the same item at the
same time will fall outside of this personal exemption. In theory, U.S. Customs
agents can remove the offending trademarks, possibly by even grinding them off.
Ouch! But you shouldn't trigger this reaction if you aren't trying to import
more than one of each item for personal use. But beware if you are bringing
back more than one of the same item per trip by yourself!

Some importer and retailer postings and pages suggest that your photo equipment
is subject to being confiscated or destroyed by U.S. Customs. I have yet to see
a documented recent case of such confiscations of photo equipment being
imported into the U.S. for individual use (e.g., under the trademark item
exemptions since 1990). Similarly, the last case I have heard of trademarks
being ground off photo gear being imported into the USA by an individual is
more than 20 years ago.

Even in the case of one photographer who recently imported 3 sets of various
trademarked goods, the U.S. Customs service only passed on his name to the
local trademark holder. The U.S. Customs service didn't confiscate the goods,
didn't grind off the trademarks, and didn't hold up the gear's entry into the
USA. The trademark holder corporation sent him a nasty threatening letter. He
could have avoided even this minor irritation simply by learning about the
exemptions and importing just one of each item per month.
</quote>

Bill