4-22-06
I got sick of seeing the warped pickguard on my 54 strat and after reading an article in VG magazine some months back about flattening warped plastic guards I decided to give it a go, with almost disasterous results. The article called for heating the plastic in an oven on a cookie sheet at 250 degrees and then compressing between two books until cool. Unfortunatly the method failed and warped it badly in other ways, however it did reveal to me the cause for the initial warping.
When I bought the guitar years ago the seller told me he had a freind piece together the badly cracked guard and in so doing glued a thin film of plastic to the backside of the guard to reinforce it. The glue probably not unlike model glue heated/melted the polystyrene guard causing the curvature. In the oven, the two types of plastic likely heated at different rates causing curving and shinking in an unexpected manner.
To now rescue the guard I've scraped and removed the reinforcing plastic from the original polystyrene guard a super glued the fractured parts together. Using a technique I saw Dan Erlewhine use in another article I reinforced the cracks by super glueing strips of paper from a set of strings. That seems to help hold it together better.
The trick now is to flatten the guard back to its original shape (hopefully). I'm thinking of getting a couple of panes of glass, sandwiching the guard between them and either going back to the oven or applying a heat gun. More to come....

4-25-06
I got two panes of glass from the Hardware store and sandwiched the guard between them. I then put it back in the oven set to 170 initally and gradually inceased the temp over a half hour to 240. I eventaully added a glass mug on top of one of the panes aboved the most warped area to apply more weight to it. When reasonable flat I removed it and sandwiched everything between two heavy books to cool. The guard is not really usable now. The heat created some slight shrinkage around cracked areas and the ther is some distortion preventing proper lineup. Time for a replacement.

4-29-06
For starters, I was able to obtain a sheet of polystyrene that's .060 thick. Now I have to find someone to cut the pickguard to 54-59 specs.

5-22-06
I had the polystryrene cut by Bryan Boots in CA. I got it back today and installed it. He did a great job cutting it and it looks pretty good, if a tad new, but 10 times better thna an off the shelf vinyl guard. It'll do for now.