Alright mate. To be honest i think that
GW plastic glue is

terrible. I have bought a few batches and i had the same problem as you any pressure or impact and it breaks. If i where you i would try and find a model train store and buy plastic cement, for me it works a lot better but takes longer to dry as it melts the plastic together. Also if your going to your local take your Dreadknight and the glue that dosent work get a refund for, then try the thin glue in the shop if it still breaks at least you can get refunded on the spot

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EDIT - Grammar