Can fail - as shown by losing water and a white steam trail behind on start-up.
Whilst the best solution is to fit a new gasket, this requires considerable skilled work.
Certainly as a temporary repair, it has been found that "Steel Seal" from Halfords can save time and money in at least the short-term. It is expensive (£40) but beware cheaper versions which may not give the same result.
I haven't had a head off yet, but being overhead cam and with a cambelt etc to dismantle, it won't be a two-minute job.
Alex Baker says: just did mine (1.4 petrol) quite straightforward no manual needed. The only real issue is that you need to put a jack under the sump and lower it enough to get the engine mount off before you take the timing belt off.
Alex left the both manifolds on; just undid the 4 bolts from the cat from underneath the car and the bolt on the gearbox.
Also see here for cambelt replacement .