8130
An FAA 8130-3 is acceptable for a second-hand or repaired part as long as it's issued by a repair station that has EASA foreign repair station authorisation. Many US avionic shops (SE Aerospace etc) issue theses acceptable 8130s so you don't pay to put the part through a UK shop to get the right paperwork.
For in-situ S-Tec work, Gama Engineering at Fairoaks, IAE at Cranfield and Tatenhill Aviaition can all do this sort of work.