Hi Nuno, Welcome to LZ.
I drive a '99 L Series Diesel, had it 9 years, and its a great little truck. The L Series is a bullet proof simple direct injection engine. It does not drive fast, its acceleration from stand still is very slow, but there is plenty enough power on the road and for overtaking. Only the very steepest of hills create a crawl
We have plenty of mountains here in NZ and it is fine on them, even towing our boat laden with lots of camping gear. On the open road it gets very close to 40 mpg (under 7.5 l/100km).
The K Series (1.8L) petrol engines have a bad reputation for head gasket failure - and they are very poor for this and may need changing (for example) every 5 years or so. I understand though they are a 'simple' change so if you do mechanics yourself are not a overly complex (or expensive) change. Other than the HG they appear to be very reliable. There are very few problems reported on here for the K Series engines, it appears they either have HGF or are working perfectly
They have more than enough power for the Freelander on road and if diesel is more expensive than petrol (which it is in a lot of places) work out hardly any more expensive than the diesels to run - their MPG is lower, but still well above 30mpg.
Do not worry if you can't afford a TD4. They are more refined and do have the option of automatic, but suffer more problems than the Rover and offer no better fuel economy - the autos are very poor on fuel around town. The later cars though are usually higher specified in the cabin with more options.
The Freelander itself is a very reliable car. Like all cars there are those that suffer problems, but my one has been boringly reliable. The problems I have had, as I say over 9 years, have mainly been due to the ABS system - I have had to change the modulator twice. I have maintained it though, all the back brakes have been replaced, front disks and engine belts/pulleys.
I have also though suffered transmission failure - broken IRD, which bought me onto this forum, to find out why - to late
If a Freelander has had its props removed - it was due to a problem. If people say it was done to improve fuel economy, then the only way this can occur is if the VCU was faulty (overly tight) and this may have broken the IRD. Some people remove them because the support bearings got noisy - if this is the case then there may be no permanent damage. They may also have started using mismatched tyres, this is the same as the VCU being tight. It may, as you appear to know, be because the IRD is broken. firt thing to do is get under the car and see if the IRD still has the rear pinion on it to drive the prop shaft. If it has not (replaced by a blanking plate) then the IRD is almost definitely broke. If the pinion is still there, move it around - if will have some rotary movement as the gears mesh, but not lots - if should also have no lateral movement. You can also drain the oil for inspection, if it is grey (or metal is visible) this is the bearings ground to a pulp and submersed in the oil - remember to loosen the fill plug before draining as they are soft and very difficult to remove, always use a good well fitting 6 sided socket. Ultimately though the oil may have been changed after a failure and look good! Really the only way of knowing for sure is to remove the rear pinion and examine the crown and pinion gears.
Good luck.