'75 lap belt only retractor cover

[sircrunch]

I have a low mile extra nice 75 gmc. I assumed anything on my truck that is showing wear is likely something that most any truck of this age would need replaced, and would likely be easy to find in reproduction. I find that I am wrong. As soon as you open the door of my truck you are met with an eyesore. The seatbelt retractor cover is rotten plastic. This truck has the lap belt only. I was surprised to see that LMC does not appear to carry this part. Any advice?

Also has anyone ever had good fortune with attempting to "polish" the gauge lens cover? Perhaps with some headlight restore? Mine is yellowing and cloudy.