It's often dirty/corroded switch contacts that cause these problems. I don't think you have to take the door panel off as Mick suggested, to get the seat switch out. To remove the switch:
1. Disconnect battey ground.
2. Pull off the little molded seat control knobs.
3. Unclip the plasitc bezel.
4. Remove two screws to get the switch out. There's a connector on the rear; unplug it.
Once you have the switch out, it can be disassembled on a bench or desk, but be very carefull of all the little BBs and springs, etc. Your best bet may be just to use some electrical contact cleaner, available from a store in a spray can. Use the little spray straw and spray each contact area liberally while working each switch back and forth. Usually this will clean up the contact area enough for the switch to work fine again, without having to disassemble the little bits and pieces.
Let us know how it turns out.