HRU216 gearbox numbers

Today I removed a gearbox with no drive to the rear wheels , from a HRU216, a 21" mower (MATU-1008834), my question is the numbers on the side of the gear casing, do they have a meaning: Aa3-0063342

I suspect that this gearbox will have worn input drive gears, tomorrow I shall pull it apart to find out, this mower is only 18 months old.

thanks for any input.