A rear indicator bulb failed today. These are 12V 21W amber glass, filament bulbs as the flasher circuit uses the load to indicate a bulb failure. The Replacement Lucas part number is LLB581 / BAU15S. These have what's called a 581 offset pin fitting.
I'm using an orange bulbs with a clear lamp lens and it has a particular pin arrangement. Since one has failed, the other is probably close to failing too, so I'm going to replace them both.
As I tried to undo the bulb holder the whole lamp module rotated and pushed out. The glue I had used to fix them has obviously failed over the last 8+ years. I'm going to take them all out and refix them. It is a very quick and easy job to do.