If it's an old seal, replace it now. The spring is to help maintain the seal pressure. As the seal ages it gets harder and seals worse, the spring helps it work.

UPDATE>>

Since starting this thread, originally regarding a possible Sundial leak on driver front side on my 6spd transmission; ive concluded that the suspected leak there may have just been excess anti seize which was applied on the threads of the sundial. Why? It was never an active dripping leak & upon inspection, if i ran my fingers through that area, the leak seemed to have been some sort of thick grey paste, like anti seize. It all collected near transmission drain bolt due to gravity.

Sprayed some engine degreaser on that area, wiped it real good with a rag. I've driven the vehicle for a whole week now, spirited, and upon re-inspection of the site, i didnt notice anything out of whack.

Ive decided to forego replacing that axle seal for now on the passenger front side although the spring has come loose. If i notice a leak, i will go ahead and replace although in this last week, in that area, its bone dry.

I have a total of 4 new axle seals from subaru , 2 for each side in case i mess up.

Part numbers:
806730042 (passenger side)
806730041 (driver side)

When i went to subaru dealership, they state the passenger side seal is part number 806730041. They also claim that part number 806730042 belongs to the driver side. The inverse of what is stated on several NASIOC threads including this one;

https://forums.nasioc.com/forums/sho...oogle_vignette

And another thread started my member "Layvon".

Please advise.

Update:

I would like to admit that you fellas here were right. I have not replaced the axle seal in which that tiny spring came out of and upon inspection today, it is in fact leaking. Nothing major, hasn't even dripped on the floor or anything; slow leak, but non the less there is a wet spot up near axle seal on passenger side and i will need to address that pretty soon.

I have a total of 4 axle seals from subaru; 2 for the driver side and two for the passenger side ( in case i mess something up). No i will not ask the dealerships parts guy for advice as to which side these seals go on. Super unhelpful .. "well this is what my computer says"... When asked what vehicle these seals are for i gave this man such a long winded explanation that by the end of it, he asked me to be his kids godfather for the christening. Said he liked the cut of my jib, still didn't understand why a 6 speed transmission was necessary on a forester.

Anyway on previous post i jotted down the part numbers for both seals. Can someone point me in the right direction, which seal goes to which side? early 04 sti Style transmission with stubs coming out axle hole.

Can you see a stamped number on the seal face, or molded into the rubbery part?

i have not checked yet. Will probably tackle this project over the next several days since i have a second vehicle. Takes a toll on my back getting underneath car so many times.

I trust the long time users here on NASIOC and other forums than i do most if not all subaru dealerships.

Most threads ive read on the forums regarding axle seal replacements on my specific style 6 speed transmission (early 04 sti / axle stubs on transmission as opposed to CV axle) ; states to use axle seal part # 806730042 for the front passenger side, but subaru dealership computer states that ^^ same part number is for driver side front. WTF

This thread appears to give the correct info;

https://forums.nasioc.com/forums/sho....php?t=2318375

so does this one....

https://forums.nasioc.com/forums/sho...oogle_vignette

It is odd to have two identical outputs on a gearbox have different seals so I'm inclined to take the dealership's word on it.

I know people claim the seals are directional but if so that should be fairly evident when you have them side by side to compare and no other gearbox or axle or anything I can think of that uses a modern rubber lip seal has directional seals. The stubs and CVs don't have anything special about their sealing surface but I haven't put them under a microscope so maybe they do.

the 2 outputs in the gearbox do indeed have there own respective seal. 100%

The directional bit can be easy to miss......there can be small "wiper vanes" on the ID of the seal where it contacts the rotating shaft. They will have a different cant from one seal to the other.
I will guess, a seal that normally rotates clockwise (US passengers side) will have vanes that start near outer edge and move into the trans as you look clockwise "wiping lube" from the shaft into the trans.
The seals from each will look and measure the exact same OTHER THAN the little ID wipers.
Let us know what you find and if it matches my description...(guessing it will).

That's exactly the kind of feature I'm expecting. Usually it's knurled into the shaft rather than molded into the seal.