Ok, first question, diff lock. Is there an automatically locking centre diff on the p38's? Im sure there is, but not sure how it works on the auto gear box (whether it only works in low range). Could somebody explain to me how the transmisson works please?!

Secondly, some idiot has forced one of my rear headrests in backwards, so it folds the wrong way, and i cant get it out to turn it around! Does anyone have any ideas before i go mad!

The centre diff has a viscous coupling linking the front and rear output shafts, this stops large differential speeds between the front and rear, but allows for small differentials when turning corners. So this is all done automatically and is very effective.

You can turn the plastic holder located in the seat so that faces the wrong way too, then the headrest should come out.

You saved me so much more wasted time with the little tip with the headrest! Thank you very much for that. I has spent a long time trying to tease that out of there before you offered that tip!

As for the transmission, it makes much more sense to me now thank you. Im guessing the front and rear diffs are the same sort of thing, allowing limited differentials too.

No, front and rear diffs are plain differentials, however if the vehicle has traction control that acts as a limited slip diff, either on rear only pre-99, or on all 4 wheels post-99.