In the process of fixing my vans, I have learned how to fix the speedometers including the housings.  Many of these have the corners broken and need to be built up with black plastic repair compound and make it better than new.  Takes a lot of time though.  

It is an age related item, the plastic is crumbling and need strenthening.  Heat is probably a major factor too.  

If any of you need this service, I can do it for a small fee.  I may have some housings that maybe better than the one you have.  
If only your speedometer is not working, I can fix that too with a new speedometer gear that fell off or missing or broken.  It's a job of patience.  

Zoltan
425 773 4646