S3C is pretty low. It goes by seniority within priority. Back when Comair was still S3, I was #3 on a list of 90+ out of HNL, but after the change to S3C I was #25 out of about 28 coming out of SYD and had to change plans.

The priorities are S2 (mainline priority bonus days....or whatever you want to call them)
S3 (Mainline employees...and I think spouse/dependent children)
S3B (Mainline Parents/retirees/non dependant children)
S3C (Conx employees/spouse/dep children)
S3CR (Conx retiree/parent/non dep children)
S4 (Buddy Passes/OAL)

Your seniority date only matters within your priority......so if you have 10 years seniority as a Comair employee(S3C), you will be bumped by the 30 year old nondependant child of a mainline ready reserve ramper with 31 days seniority(S3. Of course you are still above buddy passes.

I'm sure its still possible to nonrev, but you have to be very careful. Also Brazil is a large cargo market where payload issues come into play.

Good luck though! I was able to get to GRU and GIG for work this year, and both were pretty neat.