Go to this thread:
http://forums.pelicanparts.com/porsche-911-technical-forum/548581-who-has-repaired-their-power-seat-switches.html
Scroll down to post #5. Follow the procedure there, it uses an aerosol can of contact cleaner with a red nozzle straw to shoot cleaner into the switch contacts thru the little holes that you expose. After spraying, you "exercise" the switches numerous times to clean the contacts. Did it a couple of years ago when most of my 8 way switches were inop or intermittent. Problem has NOT returned! I used this cleaner, THE BEST!!
go to:
Amazon.com: CAIG DeOxit Cleaning Solution Spray, 5% spray 5oz: Everything Else
Believe me, I have worked in the electronics industry close to 50yrs, and have tried every electrical contact cleaner there is. No other cleaner can hold a candle to CAIG DeOxit D5.
Many products can clean and make things work for a while, but the D5 chemical completely does away with all oxidation and then deposits a lubricant film which prevents future problems. It's what the pros in the electronics industry use!
Even if you don't get it for this problem, get a can and use it on any electrical connection you make. i.e. when replacing/reseating fuses, battery terminals, slide on electrical connections, etc. It will save you future headaches and your butt!