Spring in Oil Pan

[Dennis500ltd]

Hello, last week i wanted to change the oil and filter from my gearbox. Unfortunately i found a sping in the oil pan. So the search begun.
I found a video here on the forum and saw a spring that looked familiaire. So i took a spare gearbox and took it apart and i found the spring that looks identical. Unfortunately the gearbox that i took apart wasn't the same as in the car. I hope that the pictures make it a bit more clear.
I bought the car a while back and rebuild the whole engine so i have never driven the car. The previous owner told me he tested the whole car before he started to take it apart. I am still in contact with him and i trust him what he tells me.
Does anyone recognize the spring? I know that there are a lot of springs in the gearbox but which spring can end up in the sump??
The spring i found was placed behind the round cap of the spare gearbox.
Really hope that someone can help me, can't wait to drive the car!!

 

[gsxr]

Appears to be from one of the 20 springs for the reverse piston. They aren't supposed to pop out.

Can you measure the diameter of the wire on the mangled spring?