I recently bought an old 80-something Peugeot frame and plan to spend the winter turning it into a nice road bike. The first problem I have run into is that the ATAX seatpost is threaded/integrated (I'm not sure what the proper terminology was in the 80s). It appears to work like a threaded headset but the problem is that it is immobile (in terms of raising or lowering). When the long screw is removed the seatpost remains solidly in place. I tried to invert the frame and pour chain lube down the seat tube through the bottom bracket (I was out of WD40) hoping it was just stuck in there but it did absolutely nothing. My desire is to raise the post a couple inches. I'm hoping someone out there will know the architecture of this seatpost apparatus and perhaps give me some advice on what to do.
You didn't say whether you had tried the correct technique for a threaded stem, which is to back the bolt out but leave several threads engaged, then smack downward on it with some sort of non marring hammer while the bolt is still threaded into the wedge nut, which will drive the wedge nut free. ( Or, place a metal rod or spare, old bolt against the stem/seatpost bolt and hit the spare bolt with a hammer to save the good bolt from the impact. )
Also, I have never done a comparison or even read about one, but "Liquid Wrench" is designed especially for loosening stuck bolts, whereas Water Displacing-#40 was made to prevent rust.
I've got a somewhat lower quality Peugeot myself; an '82, I think. Watch out for unusual thread/part sizes.
