Bushveld & Matt's advice is all sound.
Have you checked that the lock pin isn't backing out? It doesn't sound quite like a broken part as the problem was intermittent at first. Broken bits tend to be on or off, not intermittent. If the pin is backing out, the sear tail can start to miss the trigger blade, eventually missing entirely. I have had several guns brought to me as seriously f***ed only to need the pin tightened up!
Dropping off the locks is fine but, if it is broken swivel or main spring, it could conceivably damage the wood as the lock is removed.
So firstly, I would examine the whole mechanism without dismantling it.
Check:
Safety - make sure it is doing on the RH what it doesn't seem to be doing on the LH. Dry fire with snapcaps.
Strikers - dismount the barrels and fire the gun against a wooden block to check you haven't got a broken striker. That might explain the difficulty opening.
Cocking - is the cocking lever (there is no cocking 'spring' unless it is '12/20' type mechanism) doing what it should? compare the two sides.
Sear - is the sear spring getting the sear in the right place to hold the tumbler? Mark the tumbler pivot with a marker if there is no cocking indicator and see if it flops around or is holding position.
Lastly, if you don't find any indication of a problem remove the locks with care over a piece of plain cloth to catch any bits that fall out.
Best of luck Mike
