how do you properly install a transmission gasket seal and axle?

This is the continuing saga of replacing front suspension and axles on a 2004 Gen 2 Prius!
I pulled a GSP front DS axle to replace it with a new Cardone axle.
2 questions related to : seating the new oil seal, and the corkscrew threading behind it.

From another thread, I took the great advice to replace the oil gasket seal at the same time as the axle - because why not add more unnecessary fun to this money pit right?!
Nothing visibly wrong with the 15 year old seal except its age.
While tugging on it with my fingers to see if I could just pull it off, it gave birth to a wire spring from its backside!
Looking at the new gasket more closely, I can see there is a wire spring wrapped around the inner flap, sure enough!
Now I have no choice - the gasket has to be replaced.
I could not re-install the coil spring without pulling the gasket off, and pulling the gasket off damaged it.

So wise and experienced Prii, while I await the delivery of my repair manual bought in duress, to see if it even has a mention of how to deal with this, please share with me - how do you properly seat this gasket?! I am not finding Toyo dealer employees to be incentivized to help me(!).

There is enough depth on the gasket opening to possibly press it in too far - or is there a too far?
I read in another post somewhere that the gasket should be installed at 2mm depth. Not less, not more - or else expect trouble!
Ok, how the heck do you do that exactly?
I tried installing a new gasket.
It is a tight fit. pressing in by hand does not do it.
Gentle tapping got it flush with the surface of the transmission housing. But the original was inset, not flush.
One more gentle tap, and the gasket dropped in farther than the original was.
No way to pull it back now without damaging it, and have to try again with yet another new gasket.
I am wondering if the variable depth of the gasket opening is meant to allow the gasket to be slightly raised (out too far) initially, then pressed in by the axle dust cover when the new axle makes contact while tapping in the axle.

In the meantime, now that the transmission opening is sans gasket, I can see a corkscrew thread.
Well, this explains how rotating the axle during the control arm-ball joint-suspension strut replacement fiasco moved the axle inward toward the engine!
But, I have never heard mention of this corkscrew design before, and it must have been designed for a reason!
What is the reason?
Are you supposed to rotate the axle in when installing it until the c-clip clicks into place?
All I have ever seen is tapping the axle in until it is seated, not rotating it in.

I am attaching photos of the bare transmission opening, front of gasket with wire spring loose, and back of gasket with wire spring barely visible in place.

 

Yes, the spring is on the inside lip.
I would highly recommend anyone replacing one of these oil seals to just go to the dealer and buy a Toyota part.
They are cheap - I paid $12 for one.
The drivers side seal is Toyota part number 90311-35054.
It's not worth buying one from Amazon to save a few bucks.
I ordered a new part online and the part that arrived was for the wrong side.
Amazon refunded the charge, but it still has cost me 2 weeks considering this is a weekend project.

From the repair manual recently arrived, there is no explanation of the corkscrew channel inside the "transaxle", but the standard pop into place is the described procedure.
Installation of the "driveaxle" is simply :
"Push the driveaxle sharply in to seat the retaining ring on the inner CV joint in the groove in the differential side gear."

As for the oil seal, these are the instructions:
"Using a screwdriver or prybar, carefully pry the [old] oil seal out of the axle bore.
If the oil seal cannot be removed...a special oil seal removal tool will be required (available at auto parts stores)...
Using a seal driver or a large deep socket as a drift, install the new oil seal. Drive it into the bore squarely and make sure that it is completely seated...Lubricate the lip of the new seal with multi-purpose grease."

So, no instructions on a specific depth, and I interpret the "completely seated" description as that sucker has to be all the way in - not flush with the outer surface of the transaxle, to be pushed in by the driveaxle.
I'll have to go find the proper socket size to drive this in with, and will post that info as well.