Hi HP,
It was a long time ago, but I think you can do it without taking off the backrest leather which is a bigger job.
If you look at the photo above, all the pumps and motors are on the front of the backrest frame. I think it may be possible to reach all those components by just removing the backrest cushion insert, which is a separate piece. You have to remove it anyway as a part of the procedure of removing the whole backrest leather.
It is primarily hooked onto the 5 hooks on the front face of the backrest frame as per picture above. You can start to get to it from the bottom, should be just velcroed at the bottom to the seat pad?
If you have a cheap ebay borescope cam it could be useful to guide your hands or a hook under the back rest pad to unhook it, although I did it by hand it is possible, but it is annoying because you have to locate things by touch.
