David,
The best way to go about is to have a sample clean prior to buying up the sofa, and I believe you will be happy to see the result.
Degreasing Procedure is simple, what you need to bring is 4 items.
The tools will be a soft toothbrush or a detail horsehair brush and paper rags.
The product to work on will be a Degreaser and an Acidifier.
You can have the two samples free to test it out, shipping is on you.
I will walk you through to finish this project as I have done to many in the Leather-Cleaning-Restoration-Forum
What do you think?
Roger Koh
Leather Doctor®
info@leatherdoctor.org