AEC did indeed have problems with the AV and AH 470 engines overheating and blowing head gaskets, often leading to more serious consequences. Having tried an increase in torque loading, a higher grade of steel for the studs, a different thread form in the block and changes of gasket material they never really overcame the problem entirely satisfactorily. In the end it was probably down to there simply not being enough securing studs in the right places to suit their wet liner engine; there being only one stud to clamp down the head between each cylinder. The Av 470 relied on 13 studs per head whereas their later AV 590, which was still a wet liner engine, had 20 studs. By comparison the Leyland 600 had 23, the Gardner 6LW had 22 and the Gardner 6LX 24 per 3 pot head.
I have heard it said that Leyland engineers considered the AEC engine as a very expensive means of boiling water.