The original design uses a gasket (that is substantially thicker than several sheets of paper) to seal the joint. This gasket also affects the ultimate position of the diff in relation to the axle housing and axle shafts. By omitting the gasket you are positioning the diff further into the axle housing than it was originally intended to be. The result is it is mis-aligned, albiet by a very small ammount. Perhaps there could be some long term ramifications from doing this?
This is true, it can act like glue if the parts are assembled while the rtv is wet. I run a small even bead and let cure for 24 hours before assembling and it works great. It doesn't leak the gear oil and can be dis-assembled and re-assembled easily multiple times if careful. Of course you need the luxury of letting the rtv cure before before assembly and the surface you apply the rtv onto has to be reallllly clean.
I have been using Permatex " The Right Stuff " with outstanding results for many applications. I don't have hours to wait for FIPG to cure. This stuff is a five minute affair and works great. Multi function gasket material impervious to any chemical solutions in automotive applications.
Figures... Why do I listen to grease monkeys? I'm an idiot. "Looks like you had some work done on your front differential and they used RTV. We don't put synth in there because it will eat the RTV and cause leaks". Toyota put in a new front diff, do you think they would use RTV? I'll have to crawl under there and take a look.