if you google 'ZF 6HP26' there is a heap of good info to digest, on Jag sites and RR sites

couple of things i noted were that if you have a 1 kmph variation in front wheel speed when going straight ahead it can give problems, so keep those tyres wear and pressures equal

some have reported that changing the fluid has made a difference ( i have personally experienced this) its recommended to do a dual flush where you re do the flush after a couple of days, apparently clutch materials can get on connectors and give problems!!

there are reports to NOT deviate from the manufacturers oil, ZF say that the trans is set up to different viscosity and drag coefficient oils to suit the specific car the trans is intended to be used in and as such using a similar or different brand oil can have varying effects

there are also a couple of PDF,s you can down load that explain how to dismantle and repair the trans and also a fault finding chart, also good reading

Ewen