That's amazing to me - I've never see a US spec SLK without power seats - especially one this nicely optioned! You would expect to see :
242 FRONT SEAT RH ELECTRIC ADJUSTABLE WITH MEMORY
275 MEMORY PACKAGE (DRIVER SEAT, STRG. COL., MIRRO
Datasheets are normally spot on, but errors do happen. I'd really be suprised that this car does not have electric seats. As much as I use mine, I don't think I'd want to be without on the drivers side for sure...
That said, if this is the only thing missing on the car, I suspect Adam would make you a good deal on electric adjustable seat bases! :-)
EDITED : Never driven an SLK without power seats. My C class does not have power seats, and they are quite adjustable (front/back, up/down, recline, and some sort of "tilt" for the seat bottom itself.)