clutch lever pivot pin missing/backing out, excess pressure in t-case

I have reason to believe that there is something creating enough pressure in my transfer case to back out both of what were explained to me as a clutch pin? They have an hex head on them and are approx 2 inches long. They have backed out and made a hell of mess of the underside of the truck. Dealer ship who partly diagnosed this without dropping the case says the vent tube is fine. Any other ideas? I feel like gambling on a used transfer case and swap it as apples to having the stealership try to diagnose and rebuild it.

edit to title to be more descriptive...

You may want to look for a hole in the rear of the case.

At first I thought pump rub, but the lower threaded pin on the passenger side fell out somewhere, there was an open hole into the case so I bought a new one muscled in back in there past the exhaust and now the same pin on the top has backed out. Do you know which pin I.am talking about. I believe it was called a clutch retaining pin. It's not one of the bolts holding the case together.

I am thinking I could remove the vent hose and the fill plug and blow some air through the hose to see if air exits the plug hole.  I should mention that the transfer case is making some noise, click, click, click, as I drive although they did top up the fluid at the dealership I have a feeling something is not right inside there, like a piece of metal bouncing around?

any other ideas,

Here is the external view

(1) Input Shaft Seal
(2) Input Gear Bearing Outer Retaining Ring
(3) Adapter Stud
(4) Front Vehicle Speed Sensor
(5) Vent
(6) Clutch Lever Pivot Pin
(7 ) Front Case Half
(8 ) Location Pin
( Location Pin
(9) Input Gear Bearing
(10) Input Gear Bearing Retaining Ring
(11) Annulus Gear
(12) Annulus Gear Retaining Ring
(13) Clutch Lever Pivot Pin
(14) Front Output Shaft Bearing Retaining Ring
(15) Front Output Shaft Front Bearing
(16) Bracket
(17) Access Hole Plug
(1 Right Vehicle Speed Sensor
(19) Case Half Bolt
(20) Rear Bushing
(21) Rear Output Shaft Seal
(22) Fill Plug
(23) ID Tag
(24) ID Tag Screw
(25) Drain Plug
(26) Rear Case Half
(27) Front Output Shaft Rear Bearing
(2 Wear Clip
(29) Left Vehicle Speed Sensor
(30) Control Actuator Lever Bearing
(31) Control Actuator Lever Retaining Ring
(32) Actuator Encoder Motor Insulating Spacer
(33) Actuator Encoder Motor
(34) Housing Screw
(35) Motor Cover Screw
(36) Actuator Cover Plate
(37) Actuator Seal
(3 Range Select Position Sensor
(39) Actuator Housing
(40) Actuator Encoder Motor Bolt
(41) Actuator Encoder Motor Location Pin
(42) Front Output Shaft Seal
(43) Front Output Shaft Bearing Retaining Ring

I have been looking for that schematic, #6 and #13 are the bad boys that are backing out, they are threaded so something must be bad inside of there right?

thanks so much for the pic

Now that I know the proper name of the pin a quick Google search shows up I am not the only one with this missing or loosened pin. seems most have installed a new pin and refilled with fluid. They have not been back to the forums to update if things grenade on them down the road though.  I think I might drop the case retighten the top pin, check the vent hosing and cross my fingers...

So the dealer cracked the case open and found way to much play on the clutch lever and the piece it was holding (neither in the above diagram) the movement is what caused the pins to back them selves out.  As for the rest of the damage, because the bottom pin was out on the highway before I noticed it, too much fluid drained out the clutch pack overheated and was toasted.  the cost to repair my case was around $2600, $1900 for a remanufactured unit, and $3300 for a shiny new one. (prices include labor) I found a dude parting out an 04 2500 Silverado and bout the case from him for $450.  Dropped it off at the dealer this morning and its been installed, fingers crossed I have no issues with the used case as it had 160000 kms on it my truck has 197000.

Thanks for the help guys, cheers!

The 1900 was about the right what I paid when mine went out due to the pump rub issue I had on a 1200 mile road trip. By the time I notice something I was still 400 miles from home.

If you are handy as such things it's pretty easy to change yourself ya just need a lot of muscle.