My 780 that I recently bought has the same problem---and they are broken, not crumbling from long term exposure to sunlight. 780s have Carello lights, which are made of a much higher quality plastic than the Cibies on other Volvos. I should also mention that these lights are unique to the 780, and VERY hard to find.

As to the wagon that is the subject of the original post---see if you can get the name of the owner from the shop, and offer them $100 for the title if you can track them down.