True, its not a big deal but wouldn't it have been nice to have known this before for the many who found out the hard way? The prior owner of the K bike I own had this failure occur and it was an expensive experience for him.
There are 2V Brick maintenance schedules—both official and rider-created—all over the Web; finding them isn't much of a challenge if English is your first language. Attached is BMW's official schedule, but frankenduck's site at
classickbikes.com is chock-full of tips and has been around for years.
Ted Verrill also created a helpful site.
Back to lubing the driveshaft: unlike most autos, the Brick driveshaft receives significant protection by being located inside the swing arm, so lubrication is less likely to be compromised. That location also slightly impedes using a zerk fitting on its distal end; however, there are replacement driveshafts with zerk fittings for the u-joint. A significant development since the 1930s is the widespread availability of molybdenum paste that when applied correctly has a transmission input shaft/clutch hub lubrication life of tens of thousands of miles without replacement.
Replacing the z-tube is a nothing-burger; in a well-traveled Brick it also has a life of tens of thousands of miles, too. In a Brick that's mostly idle, it will rot.
Relative to stokester's observation, I'm using Ted Porter's spline lube—actual manufacturer not verified—but Loctite 8012 would be my next choice. The prices are similar but it would be another 60K miles before I'd need more than 2 oz from doing the driveshaft every year and the transmission input shaft/clutch hub at 30K–40K intervals. Only Porter seems to supply small sizes. Staburags from Amazon sellers worked well for me during the first 80K. I believe it is a Barium/Graphite compound. Graphite and Molybdenum have some similar uses and lubricating characteristics.