That said, there are a few things from what I'm reading that don't make sense to me.
For example, you state that according to your testing only about 15% of units have this issue, so the vast majority (85%) are apparently operating correctly. In fact, you state that you have 'sufficiently tested and validated' the stock that you have and they are operating normally. You also explain that the issue is software-related and Sangmutan are working on a fix. But here's the issue:
1. If the problem is simply software-related then should not all units be faulty, as all units presumably have the same software? If the issue was fixed at some point in the past with a software update then why have Sangmutan been unable as of yet to release fixed drives?
2. If the problem is a combination of a software glitch and the use of particular hardware would it not be a simple matter to isolate the problem hardware and avoid it in new units? Why bother with a software solution if the issue can be truly solved with a change of hardware?
3. If it's a matter of some component(s) being out of spec causing the trouble then, besides simple QC steps to solve the matter, if your testing method were truly effective would not a relatively simple solution be to test each unit in an overload condition, verify that it functions normally, and then release it?
3. If 85% of all units are trouble-free, why would you bother replacing units that you know (ie. "have sufficiently tested and validated") are working properly?
4. The controller runs a dsPIC. You state that "the micro-processor improperly shuts down the driver and may no longer be resettable". If that's true, a) how in the world did they manage to lock up a PIC in a motor controller application, and b) would it not be a simple matter to reload the program to the PIC in Toronto and send the controller back out?
5. You state that "[p]rior to discovering this problem, we did not test for torque" and that "[i]t has always been Novakonís policy and practice to screen and test all machines in our facility against a list of accepted standards within our testing capability before shipment to our customers". It's a massive oversight to have a brand-new drive system and then not bother testing if it's satisfactory. That really raises questions as to what else you've overlooked.
6. You state "We would like to assure our customers that since it is our policy to integrate and test our machines in Canada, we can react to these types of problems immediately and effectively. Consequently we do experience longer shipping delays due to the more in-depth testing ..." I'm not quite sure what you mean by these statements as they seem contradictory at first glance, but obviously the first sentence is not correct in this case. Your 'integrating' the machine in Canada in no way helped you to "react to these types of problems immediately and effectively". You are at the mercy of Sangmutan in China, and many customers who have had this issue have had to wait a very long time for any kind of a solution.
Frankly, though, I don't think that you and/or Sangmutan truly have a handle on this problem, as evidenced by the still absent solution and the seeming inconsistencies, but I think what is/was far worse is the delay in acknowledging the problem and trying to work out reasonable solutions. The implication has been that the problem was the customer's fault, or at the very best not Novakon's responsibility, and even in the comments above (eg. "In our experience using these machines, we have not exhibited a high failure rate as reported.") the tendency is to downplay the problem. Owning up to issues will win respect, but covering up issues destroys credibility.
Having said all of that, I do appreciate that you've stepped up to the plate and offered the temporary replacement drives for affected customers, as well as the upgrade when/if it becomes available. But in my opinion a lot of damage to Novakon's reputation has been done because of poor communication and a slow initial response. Consequently, I think there's likely to be some loss of good will towards the company that will take time to build back up.