I just added a couple of pages on the website on tightening up the tolerances on a 915 shifter. These modifications aren't really necessary for day-to-day driving, but they add an incremental amount of shifting ease and accuracy to the factory shift housing. For those of you who wish to find out more, go here.
Regards,
Sherwood Lee
http://members.rennlist.org/911pcars
www.seinesystems.com
