Gather ordinary evidence
Photograph the whole unit, operating stopper or air button and any accessible label. Old paperwork may show a complete reference without moving the appliance.
Keep uncertainty explicit
The enquiry may need inspection before parts can be identified. Do not choose a motor, seal or stopper from colour alone. Describe the fault so suitable assessment can still be considered.
A useful distinction
A service sticker can contain a previous contact number rather than the appliance reference. Preserve it, but distinguish its text from manufacturer information so an old service record does not become a false model identifier.