With ribbed case final drives the hole for the brake cam shaft was exposed to the final drive oil presumably to provide lubrication. 2 or more O rings were fitted in an attempt to keep the oil from leaking out.
Has anyone heard about this? I find this facinating
Not only does the final drive oil lube the brake cam but it does it well enough in some cases to have earned a reputation for leaking out and contaminating the brake shoes. This is why there were changes in the number of O rings in an attempt to keep the oil in. In 1985 BMW gave up and sleeved the hole so the the brake cam reverted to the pre 81 situation where it needed to be greased. They wouldn't have done that without a good reason.
