I remember many years ago (in the early 70's) I had a 61 Polara Coupe with the same problem. I remember removing the light bulb and drilling a hole in the pot metal housing so that the heat had a place to escape. I bought a new lens for it and it never warped after that. I traded that car in for a 71 Swinger, and now I wish I could find another 61 Polara.
Of course my reproductions will also warp, poor design of the light I am affraid with no centre support, so if I can make them to a better design i will so that does not happen.
The other problem is that the bulb is a 15W (# 1004) which give a lot of heat very closed to the lens !! Remember that the map light is illuminated every time one door is open .. If you leave the door opened several minutes the lens becomes a little .. soft.
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Philippe COURANT (Pau, France)- Webmaster des sites ACCF et C-I-F
Imperial 1957 Crown convertible
Buick 1996 Roadmaster wagon
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