Robomow, I also am a newbie. Not an experienced re-builder like some here. But I am a watchin! Sorry that I cannot help you with the source of the cogs because I have not replaced mine. They are original. My Rover came in undamaged condition from a great chap in our Adelaide Hills. (The only problem with these engines though is the strength needed to pull starter cord javascript:void(0)).
I trust that someone else will reply to your question as from what I have seen ODK is pretty good at advising such stuff. regards Chris.
