Rav4 T180 - spring behind transmission bolt

[Jpadie]

i was trying to drain the transmission of most of the fluid and didn't have a 24mm socket.  So used a torx driver to remove the torx bolt just above and to the front of the drain plug.  

out popped an unfortunately small amount of oil, a spring and a sheath that went over the spring.

any thoughts on what the spring and sheath might be?  putting them back and then trying again, I have the sheath even more unfortunately remained in the transmission and I now have only the spring and bolt. 

none of this is fatal as I have to remove the transmission anyway, so can fish it all out and replace. I'm just curious about what it is.  The spring was not under any pressure at all.