Just to chime in with a side opinion, these transmissions probably shouldn't be shifted quickly - that is - trying to shift between first and second (or other gear combinations) as fast as possible. When you do that you are not allowing the synchronizers to do their job, and even if they do you are stressing the system more than required.
When you jam the gear shift stick from one gear to the next, it causes unnecessary wear to some internal transmission components.
Just do normal "old-man" shifts.
(spoken by an old man.
)
Ken300D