Hi pasadena_commut,

Glad to hear your LBS was able to solve this with a simple shim.

Just to clear up something, I don't believe that handlebars and stems are supposed to have splines that engage in a lock-and-key fashion. It's been awhile since I've looked at a handlebar/stem interface. If I recall, the handlebar had some horizontal texture on it, but the inside of the stem was smooth. This was for a Nitto quill stem and Nitto drop handlebars, which is a rather different setup than yours but a high-end one that has never given me a lick of trouble.

(Someone correct me if I'm wrong.)