Thermostat leak at head 1.4mpi

Saw a puddle of coolant resting on top RHS of engine. Initially thought it might be the headgasket, but after some feeling around with tissues and going ouch while the engine was hot, it seems the thermostat is leaking at the cylinder head while under pressure. Surprised as the thermostat is under a year old with the new o ring supplied. Might have shifted out of place during installation, or gone hard and flattened out with engine heat.

Was going to do the obvious, i.e. remove thermostat and replace o ring, check for cracks in thermostat etc. Just wondering if there was anything else that could be causing the leak in that area I should look out for whilst the thermostat is off. Particularly as the car has had a long-standing coolant-loss issue (which I thought might be headgasket). Planning a long journey shortly and would hate to empty my coolant during it