Lorna, I have exactly the same problem - I think it's a design flaw & the composite used to make the trigger moulding isn't up to the job.
I think I'll be manuafacturing one out if steel & hardwood or possibly aluminium extrusion. It appears there isn't anywhere to buy specific parts of the Royal DS5 mechanism.
I can answer this question...
Einhell garden sprayer ROYAL DS5 ?
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