how to clean a large stain on the leather of my Relling's Siesta ?  

Cleaning up the leather..
Saddle soap will remove some of the stain, though not all. That looks pretty deep but I would give it a try anyway. You can also remove the wax with a remover and then re-dye the leather also. The same folks who sell shoe dye sell wax remover. Sounds like work but worth it in the long run as they are such comfy chairs. Once you redye you will have to apply polish just like doing a pair of shoes. Then you buff.. If money is not an object you can actually by new seats though the last time I priced them it was prohibitive.
Good luck

any other recipe ?
Thank you Hazelnut. By "new seats" you mean spare leather parts ? Where did you see them ? Any other recipe for cleaning leather around ?

?
Could you "dye" all of the leather dark brown/black?
just a thought.

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I contacted this company when I was thinking about dying the white leather cappellini benches scored a few weeks ago, they were excellent, really good prompt advice, give them a try.
http://www.fiebing.com/

thanks Heath, I checked it...
thanks Heath, I checked it out, maybe I'll find a similar company in Europe.
Mark, thanks for the help, I am not sure that dying it darker will make the stain disappear thought. I would like to make it go away first

Westnofa
You can go to Westnofa.com and order new seats. However, not cheap.
Hazelnut

Westnofa
I found my original tag for my Westnofa's and here are Eu phone numbers that might help. Tel. 70 25 11 22 and another at Tel. 70 06 10 and a fax 70 06 80 51
I tried to locate the site where I saw replacements and could not find it. It's been about 15 years since I bought mine at a Scandia store in Berkeley. I purchased my second set at a local thrift store and didn't like the color of the cushions. After finding out the replacement cost I learned to love the salmon color.
Good luck...