Judging by the lack of recent activity with this thread, it appears definition of the true defect seems elusive. Definition of an effective rectification of said defect seems equally challenging. Bogie replacement seems to be the panacea.
Despite Trainorama's best efforts, perhaps the lack of news re a factory fix is indicative of a lack of factory interest. Sadly we may have years to wait. A free or low cost rectification within a reasonable time is but a dream.
'Fitness for purpose' and 'merchantable quality' come to mind. Australian consumer law does not place a 'warranty' time limit on goods so regardless of when purchased, a return for refund of defective goods to a retailer (or manufacturer) is always possible within a 'reasonable time or use'. Even a receipt isn't necessary especially if a single supplier. One or a thousand faulty units makes no difference to the fitness or merchantable test.
With 7 of 9 locos defective, I think I am entitled to describe the internals as being 'so very bad'. It is a fair bet that most if not all of the DE's have or will have the fault.
If an effective fix could be designed and proven locally (within Aus.), I for one would be prepared to contribute toward a sponsorship ... but with a depleted manufacturing sector and lack of fine scale engineering capability, it may be futile. I wonder if a local manufacturer might find it a viable project to build replacement bogies if there was sufficient pre-commitment by holders of faulty units. Has anyone including Trainorama been down this path?