The manual is for all slant needles, but has parts near the end for specific models. Here is a link to the manual:
http://www.parts.singerco.com/IPsvcManuals/306W25.pdf
Your stitches are beautiful. Last night I spent a good amount of time with the top off of the machine, watching the locking tabs and the cam followers. The locking tabs are in the slots, and the cam followers are moving with the ridges on the cams. Now the problem is that the pattern as it is sewn is stretched out . For example, when choosing BR or HL, I can see that the stitch is in a pattern following the shape of these, but the stitches are far apart, more similar to a zig zag then say a embroidery or satin type stitch. This is an improvement from before, but still not right.
Do you think it would help to use some kerosene to clean the cam stack further? And did you take your cam stack out to clean it, or did you clean it in the machine?