Same, only difference is the X ring has 2 sealing surfaces and O ring only 1. As far as a sales man, he is just that, a salesman not a mechanic. He is repeating what he is told and the people telling him want to sell lube and chain sets etc.. and he himself wants to sell.

I learned all I need to know about life by killing smart people and eating their brains.
Eat right ,Exercise ,Stay fit, Die Anyway!