Try our new info resource - "Aladdin's Cave" (Main menu)Just added a separate link to Ash's Dropbox thread (shortcut)
Have you tried Nurse Julie I bought my 400 pump kit from Julie?
Is the gear change seal flush with the case ? If you push it too far back, there is a oil channel that can be blocked by the seal and if this happens the oil is not feeding the internal parts. Engine will not last long and the seal will leak
Looks like an O-Ring chain, make sure there is clearance for it. Seal looks ok, looks dry as well.