I just converted my 10V 2nd gen right Ergo to 9v by buying a right Ergo that was broken with all the parts attached. The key is in the video above. I found the down shift toothed ring has a front and back, It needs to be oriented correctly. In addition, the sequence of moving the up shift is key to not having to fight the spring upon installation. The last key is the positioning of the part the spring is locked into. I mounted the Allen key used on front in a vice for mounting the assembly. Made the installation much easier.
P1050430 on Flickr
P1050433 on Flickr
Left overs. Note the downshift lever ring is in backwards. If one of your bearings falls out, there is a thick washer that goes between them. You should be able to assemble and tighten the screw and still shift fine.
P1050434 on Flickr