They are not meant to come apart which is why you are having difficulty removing the circlip. The gear is a press fit on the shaft, you may be able to remove it by heating the gear and prying it off but be careful. When the were around ossa only sold the water pump as a single unit, you could not buy just the seal. I had an issue with one once that had to be replaced so I took the old one apart with brute force which is how I found out about the press on gear. I bought a couple of spares after that just in case
buy one of these: https://bvm-moto.co.uk/index.php?route=product/product&product_id=2061
The new type filters are easy to remove but this thing is even easier and keeps the actual filter spotless
Looks like he just pulled the filter out and took the picture of the water that had soaked through it from all the mud that got thrown up under the fender. If the kit is cheaper than a new fender I would just buy it, I heard they were definitely mor3 flexible than beta originals.
I would definitely argue that as it is not racing. Where I live there is a bylaw that states racing of motor vehicles is prohibited but I never have any issue pottering around on my bike
Another suggestion would be the fuel pump connector at the base of the fuel tank, it is very succeptible to water and corrosion, clean thoroughly and pack it all with dielectric grease, also do the same for the CD I unit
Put the word out to see if anyone close to you has the cables and a laptop and can meet up with you. This is exactly the reason why they should have sold the bike with the cables in the first place, unfortunately there are few owners with them
Engines were an ossa made item but many of the parts appear to be common as they were designed by the person who designed the gas gas engine I believe so there may be some cross over, likely for more common parts