I wish I could help with identifying what kit will fit. Have you contacted Mini Spares to see if they have a kit to rebuild the reproduction Mk1 servo they sell. Perhaps it would work on your servo.
A decade ago I bought a kit to rebuild my car's servo. When I opened up the servo I found it was beyond repair. I sold it for parts along with the rebuild kit. I used the proceeds to buy the reproduction from Mini Spares and have been happy with it. The Mini Spares reproduction is their number 21A1293. The web site says it is out of stock but it might still be worth telephoning about it and whether they have a rebuild kit.
EDIT: I forgot to mention that certain Alfas from the 1960s also used a version of this servo and the reproduction part for the Mini was probably from Italy. You might find some of the information in the thread linked below interesting. You'll recognize the servo in the pictures and they identify sources for it. Those sources may also have rebuild kits that might work.
http://www.alfabb.co...-rebuild-6.html
Edited by dklawson, 06 February 2014 - 12:57 AM.