The ones in my old Passat packed up, but that was 8 years old, so kind of expected.
The repeaters are sealed LED units that from memory cost around £20 each. To fit them you need to dismantle the mirror. You need to unclip the mirror glass, undo the motor from the mirror housing then take the cap off to gain access to the repeater retaining fixings. There are plenty of online guides with pictures if you do a search.