The gear parts that you are after are HERE If the gaskets are ok then don't worry about replacing them. The other thing that I would replace would be THIS and what we normal use to clean the carby is HERE .
As to the Disc I would expect it to fit any Victa 18" model but for the VC160 you would not be able to get a mulching plug.
Regards,
Bruce
Please do not PM me asking for support. Post on the forums as it helps all members not just the individual.