Take the cost of buying used gears, A
add the cost of replacing said gears when they fail, B
A + B = X..if X is more then the cost of doing it right..you don't buy them.
seriously though. the gears cost nothing to installation, so might as well get new ones with bearings and etc too
thanks for the input. ya im gonna buy new ones, i want to know for sure they are perfect, not taking any chances. if im gonna do it, i gotta do it the right way.