Hind sight is 20/20!

I installed gasket twice glad i did ! (just the bolt tightening 2x).

What was GM wrong?

1) gasket deteriorated
2) rear coolant passage had orange gew
3) block was eaten away and pitted where coolant gew was (aluminum side ok)

What i saw caused failure GM did NOT tell you:

1) plastic gasket
2) coolant + oil + rust makes gew, not mixing coolants. it eats your head! (change before 135k mi. even if not yet leaking !)
3) aluminum intake WAS NOT MACHINED (machining marks uneven and like .005" tall, meaning after surface prep i still had lands and grooves)
4) dissimilar metal contact causing rust - and gasket does not cover full area like a head gasket would

Why did i re-install gasket what did i find?

I forgot to tire lube gasket wanted to see if i pinched it. no. but should check. Always use soap so they seat well! Gm did not say use soap but you do trust me.

I found head rusting. Also bolts had loosened (settled, i shoudl have used soap).

So i re-cleaned head put a very thin (almost can see metal) rtv coat only on head side and laid gasket on it. none on aluminum side (will come off easy if ever). AND USED LUBE. did tightening sequence gently many many times (V needs it). that not only helped seal pitted areas but (i hope) will prevent dissimilar metal contact and rust development.

Why? it'd rust (esp. with dissimilar metal contact!) worse after time and grime. That'd definetely cause a leak.

Intake is the most critical for performance it's very high vacuum/torr. and on any seal if any fluid or dirt gets under gasket it allows more to get under, which then fails.

I let it sit overnight the bolts were still tight no problem.

Engine started right up no problem (sometimes a little driving/heat is needed after to seat gasket on some cars) (actually i goofed distributor re-did, and had injector clog re-did that - but 5 worked very smooth anyway).

I later quickly tested for leak with carb cleaner: no leak.

What i did was similar to what many have done, plus i had recently done it on another vehicle.

I suggest youtube also:

How To Replace Intake Manifold Gaskets On A GMC Jimmy 4.3 Liter V6 To Fix A Coolant Leak - GM Truck Engine Repairs

I saw that after install but like his write-up.

 

before i did the job there was NO air leak. only "coolant consumption". also noted: A bad leak would allow coolant to drop onto cam ! One more reason not to wait to do this job after 100k mi or any coolant consumption.