3rd gen T4R dilemma

[stir_fry_boy]

So is overheating the primary cause for blown headgaskets? Are there any major reasons on 3rd gens?

Overheating is usually a symptom of a bad head gasket. Overheating warps/cracks a head. Some times a blown HG is caused by wear and tear alone, sometimes it's caused by not using correct coolant.