As I mentioned last time, I had to take the van in to Doherty Clark because the mechanic and Tyrepower couldn't get the caster right on it. I was told that Doherty Clark in Sebastopol were the people to take it to because they did a lot of light truck and heavy truck suspensions, but when I rang them they told me to contact the Ballarat location, so I made an appointment there.
Spent the night in Ballarat so I could get in there bright and early... and they can't do it. The person who took the appointment paid no attention to the fact that there's no way a Mercedes Sprinter would fit in their tiny shop! They recommended I try get an appointment at TrueLine at Latrobe Street (who by the way have a terrible website).
I decided to just pop around there, and I lucked out - he had a no-show and managed to squeeze it in. He seemed very switched on about steering matters, and was rather happy with the alignment job Tyrepower did. There is apparently no caster adjustment on the Sprinter, and I still have a negative caster. He brought up the fact that there are blocks under the rear leaves, and that maybe they weren't stock - I'm wondering if they're a result of an ambulance conversion.
So I'll have to try work out if the blocks are stock, and if they're not see if I can remove them and the van should handle significantly better.
Update: I learned via a forum user that the front crossmember can actually ovalize it's locating hole and shift backwards. Using a special jig, it's possible to shift the thing forward and correct the caster. Now to just find someone to do it, because I don't particularly feel like messing with it.