I'm not sure if the seat can be moved manually, but I've had the same problem before. It usually means the switch is broken or the contacts inside are dirty and/or worn. If you are comfortable doing it, you can remove the switch and open it up. If it is like mine, there will be a series of brass levers, springs and ball bearings inside. Usually these get dirty and worn with use. You can clean the parts with alcohol and reassemble, sometimes switching the parts around a bit. Worked for my car.
Alternately, you can replace the switch itself. They're not too expensive.
2007 E550 4Matic - 61,000 Km - Iridium Silver, black leather, Sport package, Premium 2 package
2007 GL450 4Matic - 62,000 Km - Obsidian Black Metallic, black leather, all options
1998 E430 - sold
1989 300E - 333,000 Km - sold
1977 280E - sold
1971 250 - retired
"And a frign hat. They gave me a hat at the annual benefits meeting. I said. how does this benefit me. I dont have anything from the company.. So they gave me a hat." - TheDon