B668 Century motor shaft o’ring


May 5, 2018
Baytown Texas
B668 motor long shaft. I think a Polaris pump using PS 1000 seal. My question is which o’ring do I need to get ? I ordered the wrong number. I’m trying to find the right one at hardware store. I need it today. Should it be somewhat loose on shaft or tight? Should it fill the whole groove of the shaft? Is it supposed to touch the ceramic ring of the seal? Thanks Bradford