For those worried about using non OEM parts, here is a link to "Managing Medical Devices" from the MHRA on the Gov.UK website

relevant quote

"To ensure that replacement parts are of the correct specification, purchase them
either directly from the manufacturer or to the same specification.
When obtaining replacement spare parts from sources other than the manufacturer,
you must take care to ensure that all aspects of the technical specification are met,
including, for example: physical dimensions, material strength, mechanical properties
and compatibility.
Any agreements to supply parts from sources other than those recommended by the
manufacturer should be properly risk assessed, costed and documented, before a
decision is made to buy them."