"the one behind" is a return opening for oil that gets by the rope seal. It MUST be left open.
Amazon has the rubber seal under SKF #14939 for less than $11.
Also if you do a Bing search of SKF 199 or 14939 you will find many vendors.
To be sure check with a local SKF or National seal and bearing vendor.
Edited by Chev Nut (02/06/17 07:07 AM)