as per my experience and as per my own knowledge,

for a bimetal engine (cast iron block + aluminum cyl head), the alum cyl head expands and contracts more than the cast iron block.

since yun nga, expand and contract and so on naapektuhan ang clamping force ng bolt (lalo na kung yung reusable bolts i.e. hex bolts).

the torque-to-yield (i.e. 12-point bolts) bolts do not require retightening because they have the same clamping force at all temperatures therefore mas reliable.

RTV is not recommended for head gaskets. masyado malambot ito. it is usually used to absorb and contain oil-based fluids. not for compression purposes.

tingin ko sa shellac hindi sumasabay sa thermal cycling ng aluminum cyl head yung HG na may shellac as compared to a HG w/o shellac kasi napakatigas yung shellac eh. just do a wide reading sa internet, marami ka makukuha.

just my info on this.