Yes, it's intentional. All of the Triumphs I have from that era have it, both the Perfekt and the Norm - and there are travel cases I've seen from other manufacturers with a similar effect. Of course many machines had crinkle paint finishes too.

 

What is the best way to clean one of these cases?

Laurenz van Gaalen wrote:

I use TurtleWax for that.

I'm wondering about the little crevices though.
 

M. Höhne wrote:

I don't know how a wax would clean something instead of sealing in the dirt and you are right to be concerned about getting it out of the cracks.

Sorry, I wasn't very specific. I use Turtle Wax Original, which is a combined cleaning and waxing agent. It removes dirt and does not seal it. It is pretty fluid, and does not stick in the crevices. It does stick in deeper things, like the juncture between two parts of metal for example. This is easily fixed with a teeth brush. I am very satisfied with how this stuff works, I prefer it over water with soap for most body parts, both painted and chrome.