Hi Dek I too are in a small town in New Zealand and it would be worthwhile removing both rear brake cylinders and having them relined in stainless steel. Unfortunately I am in the South Island travelling with family but had my +8 slave cylinder relined by a firm in Christchurch from Tauranga I received it back in 3 days and the stainless steel will last longer than the original with the installation of new seals. Doug
The wheel cylinder just has the Caparo number on it. The rear brake shoes that I fitted at the same time indicated they were applicable to P100 and Transit so probably the same cylinder. I believe the official part number for the cylinder to be CW15953 that should help with you local brake man.
Thanks for everyone's help. It does appear to be a from a Transit. It has been sourced and is currently on its way to me (it is in "transit").
We bought the car new in the UK where we had it for a year. It was then shipped to New Zealand where the father in law borrowed it for 3 years. We have now had it back for 9 months. During all the time that we have owned it, it has been serviced as per the manual. It hasn't been driven on salty roads.
I am not sure why only one side has rusted out and the other is ok. The brake fluid is clear. I can only surmised that it was faulty, unless someone has a better idea.