I think I need to replace the lower cam seal on the left hand side of the motor. Big oil leak into the cam belt covers. What's the general procedure and is there anything I should be aware of?

Remove timing belt and cam sprocket
Unbolt seal reatiner
Pull out seal
Ease in a new seal with a big socket

Anything to be aware of, I assume you know how to take the timing belt off... Probably just make sure you don't scratch the surface of the engine/camshaft where the seal goes.

And if one is leaking, only a fraction longer to replace them all while the belts are off, only a matter of time until the others start leaking.

Then while your at it, probably replace the crank seal, just unbolt the oil pump, put in a new seal, and put new gasket back on the pump and its done also.

Ta mate. I'm not sure that it's the seal. The seal look ok, but the rocker cover has been leaking for sure. I'm just doing the seal to be safe.