Learn to do the bits yourself, it will be alot cheaper. Defenders are farm and military vehicles, they are designed to be easy to repair, a haynes manual or the rave manual is a great guide for it but you will find its just nuts and bolts really...
I changed all my diff/box oils today, I had what looks like a gear tooth stuck to the transfer box drain plug magnet, looks like im gonna have to change that at some point soon, its running tho so no rush. I dont think this thing has ever had the oils changed, a bit of TLC though and it will be sweet, need to look out for a disco box and front axle, possibly the rear as well... Its all for the future tho...