Fan...I have a shaeffer system. I am not clear what you mean by "slips". I've never had any problems with mine. A fixed strut holds the boom at the precise angle for furling and you need to keep tension on the main halyard as you lower/reef to get a good, tight wrap. Otherwise the wind will tighten the wrap on the mandrel and leave the sail baggy. Is that what you are taking about?
BTW... I think reviving old threads with new questions is fine...but itis helpful to others if you start by saying..."I know this is an old thread but I have a related question". That way, we don't waste our time reviewing the whole thread. Thanks in advance...and welcome aboard!
No longer posting. Reach me by PM!