this is driving me crazy...please help!

[SwampDonkey]

im having an issue with my camaro. its an 1989 rs with a 2.8 v-6, and what i think is a 200 4r transmission. the transmission has started to leak, and there is a pinhole in some sort of cover. its toward the back of the transmission, on the drivers side. its this dome/bell shaped cover thats made of some sort of thin metal. i cannot find the name of this cover, or what it covers at all anywhere. under the cover is some sort of stainless rod with a small gear on the end, and a weird piece on the end that rotates. im sorry i cant explain this any better, but i have no idea what else to do haha. thanks for any help you can provide!