I could not sleep very well last night thinking how to proceed. I decided to remove the spring from the bike and check it. Maybe it could be fixed. Early in the morning I headed to the Mongol Rally Service. This is mongolian mechanic which is famous amongst the Mongol Rally riders.
He was not awake yet, so I started myself. First removed the saddles, than the alu case carriers, exhaust damper, and rear wheel. Now the spring could be removed and the mechanic appeared. We took out the rear shock and checked it. On the lower side we could see the gasket open and the bottom ring was loose. The bike has now about 27000km, so I will check with BMW if this can be replaced under warranty. If not I will replace it with a stronger aftermarket part.
Anyhow we could not fix the spring and reassembled everything. I gave a call to Mongolian Motorcycle shop in UB to check if they have this gasket but no luck. It takes two weeks to get a replacement.
Next we called the Mongolian BMW importer, but unfortunately they only do cars. There is no Mongolian BMW motorbike dealer. Then we called Russia, the dealer in Krasnoyarsk. The part is not in Moscow, and not in Russia, so it has to come from Germany. This will take up to 4 weeks.
We will ride on to UB. Still about 1000km to go and it will be bumpy. In the meantime we will think and try to find the best solution. I hope we get good news from our dealer back in Belgium.