Ciao from Italy.
Some years ago I decided to have my rear shock serviced (VStrom 650 L0).
I got in touch with a member of the italian VStrom forum who is able to work on it, adding a sort of aluminum diaphragm separating an high pressure nitrogen upper chamber from the lower oil section. What you get is very efficient rear shock, even keeping the original spring.
He also provides a similar service on the forks (I can't describe it in english) and I must say that the final result is a complete revolution in terms of stability, reliability and safety.