Here's the problem I found with used seats......
There's a little metal stamping that holds a spring in mplace in the adjustment handle. If that metal stamping is m swing the spring does not stay in place and thus the seat slides all over the place. Make sure it's in GOOD working order first.
I know of a guy here in SoCal that parts out these trucks. I know he has seats....many of them. Not sure how much but will get you info if you want.
Michael.
cigarbox@earthlink.net