My biggest complaint with my slk55 since I got it was the uncomfortable seats. As a bigger guy, with broad shoulders, they just don't work right for me. I found a set of seats out of an R172 slk55 on ebay, so I picked them up. I'll update this thread as I go with what's needed to retrofit them into an R171.
I found a couple threads on here about people putting R172 seats in, confirming that physically they'll bolt up. What I haven't seen is anyone that has retrofitted the electric seats with memory.
The seats that I bought showed up yesterday.
Bengal red seats, complete with seat heaters, air scarf, and adjustable lumbar support.
For reference, the layout of the components on the bottom of the seat
The goodies in the back of the seat
Close up of the seat controller plugs
Prior to ordering, I spent quite a while going over the seat control boxes to make heads or tails over what it going to be necessary wiring wise to change things over. The biggest issue being that the R172 seat control switches are mounted remotely and get appear to get their signals via CANBUS.
On the bright side, the seats have the same wiring connectors coming off the motors, going to the same pins on the seat controllers, etc. A close examination of the 172 seat controller shows that it has all the pins for the 171 seat switch. My current plan is to pull the seat switches off a 171 seat and try them out with the 172 seat controller. If this works out, I will mount the seat switches into the side of the 172 seats. If this doesn't work, I will wire up a 171 seat controller. The 171 seat controller is shared with other MB vehicles that have lumbar support, so I believe I can make that work in a backward compatible way.