90TD5 - fwiw I do think you need to listen to what these good peeps have said.
Ditch first guy, and unless money is no object go to a decent independent rather than a LR dealer (in fact on many occasions I've found that money is less of a consideration than skill....)
With a cracked header tank you WILL lose coolant - it is a pressurised system. Get a new one on there before you can nail down anything else. If the gasket is gone then you might get excessive pressure, but there is meant to be some pressure when running normally.
And to answer your first question, yes I did have a cracked TD5 cylinder head due to bodged head gasket job by nameless (and now defunct) dealer. New Turner head (the Spanish upgraded one mentioned above somewhere), fitted myself carefully and slowly.... and no probs since. A blown head gasket and even cracked cylinder head is unlikely to cause major damage to the engine if spotted and dealt with - you can see from the thread what you need to do in sequence to get to the bottom of that.
Listen to the good advice...! (and in my limited experience of forums, expect a few to take the P too) A