Price elasticity of demand parts for diesel engines (Perkins) - Europe
/ North America.  Needs a quality response at this price - pistons,
filters, water pumps, oil pumps, etc

Given that a lot of those parts are probably outsourced

... I would guess the PE is not that high

There is a good chance that tractors (cabs) are using second source
components without their owners knowing.

Nobody in their right mind would install a dodgy sub component in a
unit of value, but ... they might upgrade.