Got a leak coming from gear selector

I have a 727 trans and i have a bad leak coming from my gear shifter selector is the a seal or grommet there that could be bad. If so can i get this part from the parts store or will i have to go to a transmission shop. I looked under car and i could move gear selector up and down and fluid runs out. Also when i take it out of park it just falls right into drive and i cant tell which gear im in unless i take foot off break it doesnt click or anything. Sometimes when i put it in park and turn it off somehow it slips out and i cant start car unless i pull up on lever. Can someone please tell me how i can fix this problem. Thanks alot
O'Reillys has the selector shaft seal and once you drain the fluid you should be able to change the seal. Take the pan off,valve body, shift linkage and drive the seal out. I used a long bolt, 2 large diameter washers and nut to install the seal.

Shaft Seal 1.jpg