What’s this plug on a 727

[blown motor]

Mine leaks so I need to remove it and seal it.

[RacerX]

Mine leaks so I need to remove it and seal it.

It isn't a plug...   it is the band adjuster.   

I did this on my 727 a while back to stop some leaks before pulling it out and rebuilding it.

Don't pull the bolt all the way out or you may be dropping the pan to get the band re-engaged
in the adjuster.    If you disturb it you will need to note exactly where it is set now, or re-do the
band adjustment after putting it back in.   Probably best to re-do the adjustment.

If you want to avoid re-adjusting, mark the bolt so you can tell how many turns you make.

Use ATF compatible sealer on the threads.   There is a permatex product for this purpose but
the name/part number escapes me at the moment.   Run the bolt out a few threads, dry it with
some brake cleaner, put the sealer on it, and run it back in where it was when you started by
using the marks.   Put some sealer a couple of the exposed threads of the bolt near the trans
case and also on the bottom of the lock nut and run the nut back in.   Re-do the band adjustment
before the sealer sets up.   Leave it alone for the full cure time of the sealer.

Worked fine on mine and it never leaked again.

Also, if that is leaking when the car sits you may need to lower the fluid level before removing
it or you will never get it dry enough to seal properly.

[Bullitt-]

Looks like the Kickdown Band Adjusting Screw

[blown motor]

@RacerX Great description but this sounds a little more involved than what I'm willing to tackle. There is also a leak on a shaft that is visible on the rearward side of the transmission and I am told there's an O ring inside there that needs to be replaced. I just don't understand automatic transmissions so I think I'll leave this one up to the pros.

[Mr Cuda]

@RacerX Great description but this sounds a little more involved than what I'm willing to tackle. There is also a leak on a shaft that is visible on the rearward side of the transmission and I am told there's an O ring inside there that needs to be replaced. I just don't understand automatic transmissions so I think I'll leave this one up to the pros.

Automatic transmissions are fun!
It's not an o ring,  it's the shift shaft seal. 
Pull the valve body to replace.
Just the next step after the transmission  filter.  Not hard,....really!

[blown motor]

I know nothing about bands, what they do or adjusting them. I do much better with rock bands. I have no idea what the valve body looks like or what it does. I think that, for me, doing it myself is prime grounds for a getting in over my head. I'll do a little research and see what I can learn. Probably my fear is born out of a lack of knowledge and experience.
Where's the shaking in my boots emoji, lol.

[Mr Cuda]

I know nothing about bands, what they do or adjusting them. I do much better with rock bands. I have no idea what the valve body looks like or what it does. I think that, for me, doing it myself is prime grounds for a getting in over my head. I'll do a little research and see what I can learn. Probably my fear is born out of a lack of knowledge and experience.
Where's the shaking in my boots emoji, lol.

On that note,  then I'd like more description of what you got going on with your kick down linkage. Whatever that is, is not factory,  and could be prone to problems. Shifting too soon, too soft or not responsive  to throttle input.

[blown motor]

@RacerX Great description but this sounds a little more involved than what I'm willing to tackle. There is also a leak on a shaft that is visible on the rearward side of the transmission and I am told there's an O ring inside there that needs to be replaced. I just don't understand automatic transmissions so I think I'll leave this one up to the pros.

Automatic transmissions are fun!
It's not an o ring,  it's the shift shaft seal. 
Pull the valve body to replace.
Just the next step after the transmission  filter.  Not hard,....really!

Are you referring to the seal on the shifter shaft near the NSS? That's not the other leak I was referring to. That is on the left side of the transmission. My other leak is on the back side of the transmission. It's on the rear servo pivot shaft.

[Mr Cuda]

The rear servo pivot ( screwdriver) is extremely unlikely to be leaking.  If it is, the tailshaft housing has to come off, and dropped valve body out, to fix.
99% of trans leaks are shift shaft leaks dripping down on everything..
Don't  forget my kick down question.

[blown motor]

The rear servo pivot is definitely leaking. I can blow it clean with brake cleaner and within an hour there's tranny fluid there.
Not sure what you mean by the kickdown linkage not being factory. This is on a 78 Dodge 4x4 truck. Maybe that explains something.

[Mr Cuda]

You have a bolt on post in the middle of your kick down  lever and some kind of cable linkage.
Cable wasn't  factory till fuel injected cars . That's why I was asking for more information,  maybe a picture of the carb area connection.