Some additional comments from a very similar experience (in no particular order):
Is the job currently out to bid? If so, where’s the formal request for substitution? If one wasn’t submitted, then the product can’t be added to the bidding documents by Addendum. Substitutions normally can only be submitted by the prime bidders, not subs or suppliers. Have the prime bidders complained that products from any of the three remaining manufacturers are not available?
Is a credit being offered the Owner for accepting the inferior product?
What sort of relationship does this manufacturer have with the General Contractor? How do you even know the GC wants to use this product on the project? Suppose the contractor has had some prior bad experience? Just because the manufacturer wants his product on the job doesn’t mean the rest of the construction team does. And after all, the contractor is the one with the contract with the Owner, and is ultimately responsible for the project’s compliance.
Pressure from an Owner is no reason to include an inferior product in the specs. If its in there, its just as if you had intentionally designed it to be in there initially. Therefore, there’s no reduction in liability, regardless of the Owner’s insistence.
It is a known legal precedent that in the event of any potential litigation that ensues as a result of a design problem or product failure, the courts (and jury of untrained lay people) will look upon the ARCHITECT as the expert, not the Owner or contractor (even though they may have been the driving force behind any such alteration of the design, and regardless of how much pressure they may have exerted on the architect to accept it). The architect is ultimately responsible for designing the project, and with products, materials, and systems that will not fail. Period.
There might be an opportunity to present to the Owner that the rep’s whining is nothing more than a sour grapes case. There’s no shortage of compliant products, he’s just being a crybaby because his company doesn’t make one. And his unethical practices are very unprofessional and certainly no reason to cave.
Give the other three manufacturer’s their day in court; it’s only fair they should get equal time to plead a similar case against mfr #4’s products and claims. Let’s see if they concurr that their sweeps are nothing more than an “expensive gimmick!”
Ahhh - To be a fly on the wall at that meeting . . .
Have fun!