[redshift]

No experience with the Savvy trans, but STP has worked very well for me. It's important to use no more than neccessary to keep the gears wet, otherwise drag will become a factor as if you were still using grease. One teaspoon or maybe two would be plenty for the trans. I also run it in my diffcases, so much more effective than grease.

You can still use whatever silicone inside your diff cups, as long as they're sealed there will be no fluid intermingling.

You should have great results as long as you don't use too much and I recommend the STP for any gear applications!