Freelander 1 Thermostat cover leaking td4

All my coolant is vanished and turns out the thermostat cover just at the top has a leak. Happened suddenly on way home so guess it has cracked. Its a 2001 td4 es auto. Looks like changing the stat is a biiig job but is it possible to change just the cover, what would that involve? Or any other ways around it to seal it? It looks like the leak is at the top where the cover joins to the metal. Wonder if i can coat the whole thing in putty or sealant or something!?

a bit tricky but you can do it I would just check the tightness of the bolts first but do not go over board with the tightening as they are only small bolts I had this happen to me many years ago and that is what it was .