Tailight lenses due to their shape were very prone to breaking, I look at all the 70 Sport furies I see and most have a small wedge out of at least one tailight on the bottom edge from someone resting a hand against it, or the edge of a parcel etc. When I had my 70 SF it was the same way.
Good luck and if I happen to stumble on a good lens I will definitely pick it up and pass it on to those who may need it.