If it's a good old SLR have a close look first if possible.
Remove and look at the gas plug for erosion, pitting or suspiciously smooth edges to the gas cut out. Some squaddies had a nasty habit of using erosive cleaning materials to get that shiny clean look before inspection and rerturn to armory. Same habit with the piston and piston head grooves
With the barrel, gas piston tube, chamber and flash hider, check for pitting.
Open up the working parts , bolt carrier and bolt and check the firing pin for pitting and sharp edges.
The L1A1 is/was solider proof, is NOT sub MOA, but can deliver 2-3 MOA groups reliably and possibly better, if a quality build and not shot out.
The standard iron sights are simple and are adjustable
If you can get either a SUIT/SUSAT sight you will be surprised how good you can be.....
There are after market replacement top covers that provide standard rails for sight mounting.
Even if you treat an L1A1 indifferently, it will never let you down.