Gasket Replacement

I have my A833 out of the car and have been thinking about what I should be replacing while it is easier to work on.

I saw some stuff on Brewers site that I'm wondering about. Thought I would get some opinions.

1- Side cover gasket. Is this a problem area for leaking? I have no idea if the current gasket is original or has been replaced at some point.
2- Extension housing tail shaft gasket. Is this a problem area for leaking? If I unbolt the tail section, will it just slide off over the output shaft?
3- Gear shift lever shaft o-ring. Do these normally fail over time?

Thanks for the advice.