Considering the car’s low mileage this is very disappointing…

I would do the shocks first (as said assuming the leak is indeed from the shock itself), luckily the rear ones are easier than the front ones…
As for the diff, again as said before if it is ‘sweating’ oil and not actually dripping, you should be OK for now, and at any rate it is a very rugged device and will take some beating before any permanent damage is caused… but if you intend to keep the car for the long run, it needs to be tackled at some point of time.
This together with the cam sensor and the airbag light (assuming that the door rust could be attributed to a poor previous repair), does not look very good…
Your’s a 2002, my 2001 car had various items replaced under warranty, including the oil cooler, rocker cover gaskets, alarm sounder, and various other bits…
In comparison, my other half’s Toyota was purchased new in 1997 and did not have a single fault – ever… all we pay is for servicing (and fixing physically broken bits).

So sorry Opel/Vauxhall but as much as we like the Omega this is not good.
