Try this:
1) Cut your original footage as 23.98.
2) Export video without audio as a self-contained QuickTime movie using “Current Settings”.
3) Conform to 25fps in Cinema Tools.
4) Open in Compressor and convert to a clip maintaining the original settings (in 25fps), but with “Duration” set to the exact duration of the original clip in 23.98.
5) Import clip to a 25fps sequence in FCP.
6) Copy and paste the sound from your 23.98 to your 25fps sequence. Or export and re-import it if you have created a new project.
Be aware to create PAL projects the “right way” if you’re switching from NTSC: Close all projects, shut down FCP, re-open it, set your PAL-settings and create a new sequence.
This procedure has worked for me on movies up to 20 minutes. Good luck!
Petter Brox
Spain