I have a big block 727 with a B&M aluminum 4 quart more than stock pan part #10280.

I can't get the pan from stop leaking. It only leaks from the front side of the trans pan aka closest to the bellhousing.

I've done just a rubber gasket no RTV sealer.

Two rubber gaskets with no RTV sealer.

Rubber gasket with a good amount of RTV sealer. And it still leaked.

I then used a rubber gasket with a medium amount of RTV sealer hand tightened the bolts and tightened after an hour. It is still leaking. I made sure the bolts are tight, tightened a little more and its still leaking.

The top of the pan where it meets the bottom of the trans is completely flat. The stock pans have the little ridges on the top of the pans.

Anyone have problems with aftermarket pans not sealing ?

Why not go to the dealer and get the new style sandwich gasket and install it with no sealant? I have never had one leak and they are reusable a number of times.

Is it the pan leaking or the vent behind the torque converter? If oil is coming out of the vent it will look like the front of the pan is leaking.

Another vote for over full and coming out the front vent.
First it says
"727 Deep pan provides an additional 2-4 quart capacity, significantly improving the cooling ability of the fluid."

Usually 2 more is more like it and if you put a higher stall they hold less. when car sits torque drains back and makes it real high and leaks out vent and down front of tranny right to the pan.

linkage seal?

in my experiendce my tranny leaks allways seemed to come from pan gasket, and never were from there... allway linkage seal and rear band pivot seal.

I agree. All my "pan" leaks were higher. Feel around or clean it all off and wait for drips. Then touch a paper towel up above the pan.

Yep...at this point its not likely to be the pan.
Maybe the selector shaft seal?

If it really is a pan gasket leak, make sure one or more bolts aren't bottoming in their holes.

clean and dry with brake clean

throw a hand full of baby powder on the area in ?

the powder will show you the leak way before it spreds to look like it else where

I would deff use one of the new gaskets with the alum pan

I have a deep chome pan. Used the Mopar rubber gasket and not a drop on the floor. No sealer. There the best gaskets

x 2 on that baby-powder. But I don't agree at-all with the need to use any trick gaskets on a cast alum pan. Since LOTS of the sealing issues can be traced to bent pan-rails ... using a cast pan eliminates that problem.

Check ALSO the rubber seal for the throttle pressure linkage IN the VB near the shifter-seal in the case.

What's so trick about an updated factory gasket that is reusable?

....because IMO .. it is not needed. What is the current cost diff ... cork and this one that you refer to ?

$0 because you get to use it over and over again instead of the one time cheap gaskets that do have a tendency to leak. That and you can't overtorque it.

I have a cork one on my 62 since the late 70's ... R&Red the pan many times .. no leaks.

Again ... WHAT is the cost diff ?

does not matter on the cost..we are high tech with it,and keeping up with the trendy stuff

We now have disc brakes. Because there better. Things do improve with time. The new factory pan gasket is 100 times better then the cheap cork they used 40 years ago. Tell me do you still use a rotory phone?