Good news by the look of it, a good clean will confirm this. Whilst you have it apart it will be worth checking the plunger on the oil pump works. The gearbox I stripped recently the plunger was sticking and would not have pumped oil. This is critical as it pumps oil to the worm gear.
Ratchets are unlocked with pin out, see page 11 of manual. A good clean should and oil should free everything off without dismantling completely. Check pawl spring MT215 is not broken.
I am currently making up some control cables for another club member and will be writing an article for The Cultivator covering removal and fitting of same, also how to split gearbox.