The bottom cover of the engine bay is made from polyester fiber reinforced material, but does not last 25 years. The front side where the 5 screws attach to the holding bracket tend to break or wear out, and sooner or later something hits the cover and completely destroys it. Happened to me when I entered the garage with a little more speed than normally. 

I was able to purchase a aluminum version at Landsharks in Germany, similar to this:


I'm not sure anymore about the price, but it could be 200 euros or so (275USD).

I must say: perfect product. It needed a little modification to make it a 100% fit but nothing special. The two "chimney" like V shaped buts need to be transferred form the old cover and that is about it. This cover will out last the car, and cope with a hundred times removing and fitting. And I did occasionally hit something but that does not really damage the cover anymore.