The overdrive unit of this transmission was leaking around the gasket, so I bought another transmission filter and opened it up to redo it.  We did a really nice job cleaning off all of the old gasket and to reseal it we used the black RVT, which is what the Haynes manual recommended.  The first try didn't work.  Still leaked.  I just pulled it apart again and redid it.  Still leaks.  Is there another sealant that would work better?  Any other recommendations for me?  btw--how much does it cost to do one of those 5 sp conversion that you were talking about?  Is that better than doing a 6 sp?  Is there a performance increase or decrease?  

Bensonsvette:
The overdrive unit of this transmission was leaking around the gasket, so I bought another transmission filter and opened it up to redo it.  We did a really nice job cleaning off all of the old gasket and to reseal it we used the black RVT, which is what the Haynes manual recommended.  The first try didn't work.  Still leaked.  I just pulled it apart again and redid it.  Still leaks.  Is there another sealant that would work better?  Any other recommendations for me?  btw--how much does it cost to do one of those 5 sp conversion that you were talking about?  Is that better than doing a 6 sp?  Is there a performance increase or decrease?

Here's the link to Keisler's C4 page: Keisler C4 kits

As far as the difference between the 5 & 6 speed transmissions go, it's all about the final gear.  5 spd is going to have an O/D ratio in 5th similar to the 4 over in the 4+3, which should be around .70:1-.75:1.  6 spd is going to give you a second O/D beyond 5th, which should be around .55:1, which should net you a larger fuel economy increase.  Even with a 6 spd transmission, typically you'll still reach your top speed in 5th, 6th is just an economy gear.  

The Haynes manual is wrong in this instance, you should use a gasket with that pan, along with a thin film (and I mean thin) of RTV to aid in sealing.

As for the 5-speed conversion, if you go back into the older issues of Vette (I believe 2005 or early 2006), you can read about the Son of Zombie car (originally a 4+3) and the conversion to a Keisler 5-speed.

You'll definitely see a performance increase with the 5 speed, and it will be less of a hassel to maintain verus the 4+3.