Hello and welcome to the forum.
The ABS problem is usually down to a duff sensor on the Lag 1,you can do a resistance check through them to find the duff one if you have a multimeter.In rare cases the ABS pumps can cause problems,but it is unusual.A trip to a good independant garage with the right equipment to read the fault codes from the system would be a good idea to be honest,it shouldn't take long and as long as the operator of the reader/scanner is switched on,it should pin point where the fault is.
As for the second problem,gearbox failure is unfortunately a common problem on the diesel engined Laguna 1's,although it's unusual to 'come and go' like your problem has.It could equally be a clutch problem in your case,but again it's unusual for it to happen one minute and not the next.Firstly I'd check the gearbox
level (with the vehicle level,remove the plastic wing-nut headed bolt in the front of the box and
should drip out,if not then the level is low) and then check the clutch adjustment.The cable has an automatic adjuster in it which can give problems,the cables themselves can also give problems internally.It's a design fault as the cable passes through a number of tight turns on the right hand drive versions (Renault probably did it one purpose to upset us!
) and the inner cable can wear through the outer casing causing a heavy pedal,and then the cable snaps.The clutch should be light to operate,if it's quite stiff then either the clutch is worn or the cable is on it's way out.