Difficulty: Easy-ish
Time: About 1 hour
Tools: Two 17mm spanners - ring and open. Long spanners may help.
As the chart below shows, it's quite normal for a shock absorber to have traces of oil around the top. However leaks like level 3 to 1 mean the shock absorber (SA) needs replacing.
Probably a good idea to replace in pairs.
As always, apply hand-brake, chock the opposite front wheel and without the vehicle raised, slightly slacken off the road wheel nuts.
Jack the vehicle up and place on an axle stand:
(note to self - it's a good idea to secure the stand with the split pin on the chain!) 
2009 and beyond models are fitted with superdooperGoFasterAerodynamicFuelSaverGizmos to the rear suspension arms on each side. It makes things a bit easier, by removing this. Easily done with a 10mm socket.
Support the suspension arm with the jack and remove the road wheel. Place a piece of wood between the jack head and the suspension arm, to prevent damage to the arm:
(No the drive doesn't slope, must have had too much vino, picture is on the tilt).
The vehicle should feel firmly supported now. Don't gamble with this - it's not worth it.
The shock absorber is attached top and bottom with bolts and nuts. Shown here with nuts and bolts partly and fully removed.
The bottom bolt is not too bad to access, the top is the worst, which is where you may need the open ended spanner. Obviously hold the bolt head with one spanner, while releasing the nut with the other.
The bottom bolt attaches through a carrier, which in turn is attached to the wheel "hub" assembly.
The bottom SA bolt will not come out unless this carrier is removed. The suspension arm is in the way and prevents the bolt coming fully out. If the bolt was inserted the opposite way around, there would be no problem and the bolt would come out, without removing the carrier. I suspect it is done like this so that if the bolt should come loose, it cannot drop out completely.
Look underneath the "hub" and you will see two bolts:
These attach the carrier to the "hub".
Although I couldn't see how there could possibly be any relative movement, it's not a bad idea to place match marks before removing anything suspension related. It can save a whole heap of re-alignment later.
In fact, the carrier doesn't have to be removed, slacking the bolts off a little and lowering the carrier, as shown, is enough to remove the bottom SA bolt.
Once you have the top and bottom SA bolts out, the SA itself should come out easily:
At time of writing part number is 48531-42240. Same part is used for both sides (no surprise really). Always check that the part number hasn't been updated.
When refitting, the piece of metal welded to the lower part of the SA, goes towards the front of the vehicle. Some out of focus, installed SA pictures:
Replace the top and bottom SA bolts and nuts.
Torque up the SA carrier bolts to 80lbft. The top and bottom SA bolts are also 80 lbft. The bottom SA bolt is easy, but the top one is difficult to get a torque wrench to (At least with my kit), so I used "mechanicing judgement" on that one.
Replace the road wheel and the superdooperGoFasterAerodynamicFuelSaverGizmo. Lower the vehicle. Road wheel nuts are 76 lbft.
If you, can bounce the suspension a bit.
Toyota procedure calls for the rear suspension alignment to be checked at this point. Unless there is other suspension damage repair, or tyres are scrubbing, I don't see that it is necessary. It's quite an involved process too.
So, there you are. Next time the spotty "youf" in Kwikfit or wherever, tells you your shocks need replacing, thank him kindly for the advise, then check yourself and if necessary, replace them yourself. 
