I disassembled the shaft holding the conical clutch assembly and posted some information on my blog. Here's a picture of the seating surface that the conical clutch mates with.
[Linked Image]
The right one has not been worked on yet, so you can see the glazed surface that causes the clutch to slip. I already used emery cloth on the left one.

The cone clutch surface is shown below, along with all the other pieces that make up the assembly.
[Linked Image]
Read more on the Blog Post