Sorry to hear of your fate. Same thing happened to me on my KLR a year ago.
My experience proved to me that there was no good bike mechanic in Uyuni. The one guy everyone said was so good, worked out in his backyard on the ground amidst all sorts of old torn up bikes and parts. Not impressive. I gave him my shock and rebuild kit I had brought with me, but he butchered it up. I attempted to improve the repair and rode as gently as possible (is that possible in Bolivia?) over to Chile and down to Mendoza to pick up a new shock the manufacturer Fed Exed to me.

What's the matter, you don't like pogo sticks?

Unreal how bad the bike handles with no oil in the shock isn't it? I was told to zip tie a sock around the new shock tp prevent rocks from hitting and nicking the shaft, which is the cause for many shocks to leak. I followed Ken Duvals advice and never had another problem. Never rode through Bolivia again either!

I know none of my story helps you at all. If there is in fact a dealer in Salta, that's probably your best bet. I was stuck in Uyuni for 5 days trying to resolve my repair. Hey, at least it's cheap to stay and eat there. There is an American guy named Chris with a hostel who sells great pizza and great breakfasts, can't remember the name of the place, on the south side of town.

Good luck. Please post your success story so we know how you worked it out.