Surely you should not be having to bodge this it is obviously a very poor design and quality control by Grainfather. I would expect way more at the price they charge and I bet if it was one of the "Lower" quality brands it would get a good slagging off by some Grainfather owners who some seem to accept the issue because its Grainfather.
I always remember the customer service of one of the Major car brands who built up a reverse psychology of making the customer feel extra special " Oh that's unusual Mr Smith we have never had that before "that they had what deemed to be a very unexpected issue with their car but in fact it was a common fault and they were covering it up very well and not losing "Brand Loyalty"
All credit to MM for taking this on but it should be the manufacturer taking the torch and not the supplier, well done MM for your input