In a message dated 12/5/2011 1:29:50 P.M. Pacific Standard Time,  
mark at shepher.fsnet.co.uk writes:
What  happens when valves sink in hydro engines?
Install new seats, new valves, grind to spec (yes there are specs  for the 
hydraulic lifer'd stem protrusion.)  Buy a rebuilt head???   ;-D
    Loren