i would not service the sachs shock as it is not so good as an ohlins and i doubt that they can be serviced properly coz i had problem to get my services because of no spare parts so i bought an ohlins
anyway i was looking for a new wilbers rear shock http://wilberssuspension.co.uk/ (go for type 641 http://wilberssuspension.co.uk/641.php for 600 EUR) until i found the ohlins for very cheap price