I've read the sticky and worn out the search button but can't seem to find a step by step tutorial for the "spa treatment". Can somebody help me out? Thanks in advance.

 

I actually have the same question.
I've tried what I thought is the spa treatment on a test section of my interior, but I'm not sure I'm getting it right.

 

The "Spa Treatment" is just a bucket of warm/hot water, and a white towel. Wring the towel out some, and "pat" it on the leather, or wrap it around your steering wheel. Do not scrub! That will turn the leather into a suede like leather. Rinse out the towel frequently, and also change the water frequently. Repeat until you're satisfied with the results, which can take a while on some. When finished, let dry, and apply KR Conditioner, Leather CPR or the like. Seriously, on some seats, and especially steering wheels, it is going to take a LONG time to open up the pores of the leather and get the dirt and grime out, be patient, and do not scrub!