Didn't test the engine (apart from compression) prior to removing it BB.
I wanted to either rebuild the entire thing or scrap it as you suggested if the gear is no good, so I have proceeded to pull it down, but that is more difficult than I had anticipated.
I can't figure out what to do with the drive pullies as they appear to be pressed on, but I may be getting ahead of myself anyway.
I will rebuild it if the plastic gear is not broken but that seems unlikely given the brittle nature of plastic and the condition of the mower.
I didn't want to break any more than I had to in getting it all apart.
Cheers & thanks for your response
JohnA