Following is a very similar case that was defended by the original registrant. The key thing the complainant would have to prove if they are contesting the domain is bad faith. They might stuggle with this, trademark or no trademark.
WIPO Domain Name Decision: D2001-0903
In fact it's actually almost identical with the disputed domain okidataparts.com and the trademark owner Oki Data! So use that as your precedent and tell you client to tell the bullying manufacturer to shove it!