Most of the "head gasket" failures I have seen were the result of an overheated engine, warped head .. not necessarily the gasket itself.
The 89-93 SC heads actually have a thicker deck than the 94/95, not sure on failure rates between the two because there were many more of the prior ones built.
The last 3.8L NA I had a blown actual gasket on was ruptured from the coolant port into the combustion chamber, probably a combination of heat, time, maintenance. It was a customers car that actually didn't display any symptoms, the not changing the oil was what ended up seizing the camshaft, broken timing chain, bent valves ..
I did a 4.6 with a blown head gasket, it was blown out externally from the side of the block, most likely too much heat / oil leaking, oh and it was a Range rover.
Coolant changes is one of the most overlooked maintenance items, used up corrosion inhibitors, electrolysis.
And the term is Detonation or pre-ignition .. not detention.