2003 Hyundai Elantra 71,000 Miles

Has the "internal filter"

I was going to attempt to change the trans fluid and filter. Drained the fluid and pulled off the pan. As soon as I pull the pan off (gently) I see there is no filter readily available, and realize I have one just behind the solenoids and valve assembly, etc. I decided immediately not to mess with it and jus tput it back together. As I went to put the pan back on, I saw a "pin" stuck to the gasket, at the very top, between the two pan bolts. It is below where the cable attaches to the shaft, only on the cast housing of the transmission. I attempted to put the pin back into the hole, with no luck. The pin is about an inch long and will only go in half way, thus I cannot put the pan on. Since I could not get the pin back in, no matter what gear position the transmission was in. I then decided to put it back together without it, figuring it couldn't possibly be important. All back together and poof, I have no reverse, cant shift into "low" and shifting is much harder, and tight at the shifter. I took it apart again, and am still perplexed what this pin is for. I tested the solenoids with a volt meter and they are testing right on. Now I am questioning this pin's need and where it goes, how it goes, etc.

Any and all help is greatly appreciated. I have had this back together and apart 4 times now and just cannot get it to work properly. I cannot get this pin all the way back into the hole to get the pan on.

I have looked in every repair manual I could find, for pics, schematic of the trans, etc and I can find nothing that mentions nor shows this pin. Please help...