Hi, this is what I found when I was looking for a replacement SLA (I never got one because latter I determined that my SLA was not my problem). The XF SLA part number is PP170 267 054 | 2042 - the first 5 letters/numbers are the model number, the next three (267) is the group number (in this case SLA), the next three (054) are revision, and the last group is version number. If you compare the XF number to a CLK320 SLA part number PP202 267 054 | 2038 (I pulled this one from the junk yard) you'll notice that the model number is different as it should be, but the group and rev number are the same. I'm not sure how much the version number matters. When I compare the two SLA's (remember, my XF SLA is still mounted in the car), the differences I can see are: the baseplates are different, I think the position of where the linkage to the transmission comes out is different, but not sure. Cosmetically, the top trim and plastic look the same. And the little I could see of the circuit board through the top looks the same. Comparing the bottom housing numbers: XF PP170 267 021; CLK 202 267 056G => confirms the baseplates are different. My hope was that the electronics were the same, and I could swap them. Unfortunately, when I looked at the wiring harness that connects to the SLA's, the color coding on the CLK didn't match the XF's. Not sure if that means the electronics are different or the color coding used on the CLK is just different, but I didn't investigate any further. So, to be safe, I think you're stuck with either XF, or SLK 320 (certain years 2004?) parts as being interchangeable. (If my local junkyards had had any SLKs or XF, I would have grab those, but they didn't so that's why I got the CLK one. It looked like the XF SLA.)
-Jerry