Having identified the rubber and plastic Sierra lower column bush as the pile of crap it is, I decided (some years ago) to go the upgrade route to a proper bearing. It's a SLFL25 bearing which has been documented in many builds such as Cobra replicas and Robin Hoods. However, it obviously is not a direct fit to the STM/Aries. Even if I opened up the hole in the middle so that the bearing would fit in, the mounting holes are too far off. Making that big a hole would remove so much material that it would weaken the mounting. So I'm going to have to make another bracket.