I have literally just had mine apart...
It is a bugger to separate - you need a very thin flat lever to slip the casing off the little wedge shaped tangs.
Once opened, there are three little V shaped caps (like the stereotypical hat worn by Chinese ladies in the rice fields).
These caps sit on the tips of three finger-like projections built into the bottom of the round motor direction switch. Be careful that you do not drop and lose the little caps..
I was able to polish these clean with a cotton bud soaked in brake cleaner.
There is also a strange pair of rounded brass dumbbell type things under the mirror selection rocker switch.
A good polish with the soaked cotton bud cleans them up nicely.
The contact plates underneath usually only require a little rub with the cotton bud.
I spent ages looking for springs that I thought I had lost from the mirror selector switch.. but it appears that there were no springs in there to start with. - well I think so anyway, as it worked fine after reassembly without any springs.
The real problem area is the "box-like" contacts in the switch that the V shaped caps sit inside.
These get as manky as hell and fill with copper oxide and crud.
It is therefore a matter of cleaning up all the green sludgy verdigris that builds up on the copper contacts.
A good spray of contact cleaner, brake cleaner or even carb cleaner will help wash the crud away.
I also use a thin jewellers screwdriver or a taper tipped kitchen knife to scrape away stubborn bits and scrape the metal contacts clean and shiny.
Another quick spray clean and then mop / polish up with a cotton bud.
That will cure most faulty electric mirror switches.
Worked a treat on mine - awesome!!
EDIT - I have copied this post and added pictures to create a How 2. Hopefully the pictures make my waffle above, a bit easier to understand.
See Here -viewtopic.php?f=70&t=16117