A question about the transmission coolant lines that has been puzzling me for years.

This is a question about a vehicle I no longer have.

Back in 2007 I purchased a brand new transmission coolant line for this vehicle because the one on the truck was damaged.

The coolant line was the one that went from the back of the transmission housing, just above (or below) the gear change linkage (from what I remember, even though it was an automatic), to the transmission cooler at the front of the truck where the radiator was.

I didn't have any manual when doing this and so assumed that the tightening torque would be 'good and tight', like the majority of bolts on the vehicle.

The brass fitting was the bit that screwed into the transmission housing and I used a wrench to tighten it well and good.

Well, about 2 miles down the road the transmission housing, where the line screwed into it, cracked causing the transmission fluid to pour out when at idle (and when moving but to a lesser degree). I discovered this when filling up with gas.

My question is, why on earth does the tightening torque on the line fitting require so little tightening? It goes against all known logic. From what I remember its finger tight plus 1/4 of a turn (or less!). I know that the tightening specs are very small compared to the other bolts on the truck but why this one particular fitting having such a small tightening requirement? And what is the logic behind it?

I have no doubt that others have been caught off guard by this and had to buy a new/used transmission after doing this, like I did.