Hello and welcome to the forum.
In no particular order,the common problems on Lag 2 dCi's are....
Worn rear axle bushes
Bent 17'' Silverstone alloys
valves coking up
Tyre prssure sensors
Climate control panel illumination
Early dCi intercoolers splitting(post 2003 cars have uprated ones fitted)
6-speed gearbox bearing failures
Various keycard faults
Front lower suspension joints wearing prematurely
Thats all I can think of for now.
The later (post 2003) cars have many of the faults ironed out,the Laguna 2 phase 2's are better again.All of the faults above have been covered on the forum and there is an awful lot of info on them.The single most expensive and most common faults are the
problems,but these can be kept to a minimum by changing the engine
every 6 or 9000 miles rather than the 18000 miles first recommended by Renault.
Avoid early examples of the Lag 2 as they are the most toublesome,and consider an aftermarket warranty on any car.
This post does sound negative,but there are many on the forum that love their Lag 2 and have had minimal problems.I'm sure some will add their thoughts shortly.
.They are a bit of a bargain as they don't have a great reputation,so if you buy carefully you could end up with an excellent car for little financial out lay.