From memory, the one on the left looks like the beefier 2.2kw (?) I had in my van when I bought it.
Notice the dimple in the solenoid/switch casing, towards the terminals at the top. That's one of the indications of it being a sealed unit and that you can't get into it to service the contacts.
There's a factsheet on the members' area (
http://www.igmaynard.co.uk/bongo/member ... rmotor.pdf), which you've probably read. Information overload if you do a
search on here!
I think starters some have 9 teeth and some 10, but I understand they're interchangeable. You may have to adjust the cable(s) to fit as my new starter accepted one of the cables at a different angle - not much to play with IIRC.