Congratulations on your new purchase. I'm sure that you'll really enjoy your new boat. In spite of the stories you may have heard about rudder problems on the Mystere 6.0 I have raced an M6.0 now for 6-7 years and have never experienced any of the "major" rudder problems suggested by others "EXCEPT" when the rudders are not set up and balanced to the rig correctly. You will find that this is true for any and all sailboats. In fact, if you speak to any of the Nacra or Inter sailors you'll find they they too have had their share of rudder concerns in the past, there is a least one web site with pages dedicated to resolving Nacra 6.0 rudder problems. So you can see that this has been a shared concern for all the 20' boats. The solution is to simply get your setup correct.
<br>I guess my point is that there is not a real problem with any of these boats it's just that we as sailors and tinkerers make changes to the factory systems and settings in order to get better or optimal performance and sometimes the results are not what we intended. You just need to get things setup correctly for your conditions and you'll have no more problems.
<br>Now, as Mike Fahle suggested, if your boat is an older model then you can and should upgrade several of the componets, springs, adjuster screws and cams, for more reliable ones.
<br>If I can help I'd be more than happy to as I know would any of the fine sailors reading these posts on a regular basis.<br><br>