The infamous "Becker Fettkasten", Becker grease-filled chain case. All the rage in Germany at a time when chain technology was sadly lacking. Worked OK on smaller not-so-fast bikes, bikes ridden at high speeds often literally baked their chain, lots of heat developed inside. A royal pita cleaning those out to replace the knackered chain!
BTW, Laverda offered a very similar set-up for the cast wheel triples and 750 twins along with a version for the 500, turned out not too popular...
O-ring chains soon proved to be a better alternative.
piet