@Buco - I note your intended trip to the USA is still 4 months away. Perhaps by then either MTH or one of their dealers will announce a custom run of a new and improved AS-616, the functions of which all work as intended. If so, IMO MTH should provide you with one for free - after all the trials, tribulations, time and effort you've put into this (not to mention the mental anguish and costs incurred 😫) - trying to resolve the problem.
In all seriousness though, one way or another I sincerely hope you ultimately get THIS engine to run - as Mello Hudson Mike said best - "as they were intended to be used when MTH manufactured them."
Best of luck to you Peter!