head,block,gasket

Hi All,
bought a 95 manual 2.5 diesel,done all the usual ,water pump,thermostat,viscous,radiator and in all fairness it will go further before belting into the red and water just dissapears .
Is it usually the head gasket,head crack or a porous block? or all 3???????
if I do the head gasket I know I have to use a quality head gasket about £120.00,do I need new head bolts as well as the manual says to replace them as they are stretch type.
Should i instead just a fit a breakers engine with 60 days warranty? By time i buy the gasket bolts etc and then find the head is cracked id almost be on the same money.
Any of you guys have any experience of it just being the head gasket blown due to the rad being blocked?
many thanks

Never let the diesel run to the read...the head warps/cracks readily when that happens...no porous block issues on the M51 that I am aware of...

If the head is warped the gasket won't seal...and the heads can't be skimmed!

Yes replace bolts if you are changing the gasket....read RAVE it will specifiy a certain thickness depending on head measurements.

Never heard of block problems. Head failure after an overheat is not uncommon though.