I've noticed a few drips of ATF at bottom of TC. I've just recently changed it out,so wondering if it is seeping out of the drain plug.

Is there something commonly used to help seal the drain plugs in the TC or Diffs?

I remember cleaning some kind of gunk around the filler plugs of the diffs that looked like came from the factory to do this...

Yes, use rtv on all of them.

I use High-Temp RTV like Permatex Ultra Black.

I picked some up last night, and I forgot which kind was mentioned here. I ended up getting the Permatex High Temp RTV RED silicone gasket maker... Any concerns with this one?

Permatex® High-Temp Red RTV Silicone Gasket

OEM specified. Formulated for hi-temp applications, or heavy-duty use (such as towing, etc.). Replaces almost any cut gasket by making reliable “formed-in-place” gaskets that resist cracking, shrinking and migrating caused by thermal cycling. Coats pre-cut gaskets to increase reliability. Temperature range -65ºF to 650ºF (-54°C to 343°C) intermittent; resists auto and shop fluids. First generation 1970-1980 gasket maker.

Permatex® Ultra Black® Maximum Oil Resistance RTV Silicone Gasket Maker

OEM specified. For dealership warranty requirements, ensures extended drivetrain warranty compliance. Fast-curing formula. Sensor safe, low odor, noncorrosive. Meets performance specs of OE silicone gaskets. Retains high flexibility, oil resistance properties through use of a patented adhesion system. Temperature range -65ºF to 500ºF (-54°C to 260°C) intermittent; resists auto and shop fluids and vibration.

(IMO)Looks like the red may be better, it's temp range is higher. Make sure you clean the threads (male and female) very good, and let the new sealant cure according to directions before refilling it. Good luck

Thanks!