OEM G/S shocks have a life of around 20K miles if you're lucky and don't ride off road. After that, you're riding on the springs.
There is a guy in Melbourne who rebuilds factory shocks but you're better off ordering an Ikon, Wilber, Ohlins, etc since they're all reabuildable and fully adjustable. Makes a major difference in the bike too.
BMW Club of Northern California, Ambassador, BMW MOA, Vice President Vintage BMW Club