Sorry, but does not sound good, Your Discover would have ran out of warranty at 3 years from date of first reg, (?? around march/April this year), OR 60,000 miles, whichever is the soonest !!
Sounds by your post, like someone fitted a Landrover exchange gearbox ??,, 16 months/45,000 miles ago,, This box will more that likely have had a 12 months and probably 12,000 miles warranty, both of which are now out !!
I know a few years back, had a TD5 XS 2000 year,, 3 boxes in the first 3 years, the last one, was out of warranty by 7,000 miles, but under the 3 years old, NOT covered !!