Come by bearing request for seal (6)
I believe the answer is:
gasket
'seal' is the definition.
(gasket is a kind of seal)
'come by bearing request' is the wordplay.
'come by' becomes 'get'.
'bearing' means one lot of letters goes inside another.
'request' becomes 'ask' ('ask' can be a synonym of 'request').
'get' going around 'ask' is 'GASKET'.
'for' is the link.
(Other definitions for gasket that I've seen before include "Packing piece used as seal in metal joint" , "It provides a seal" , "packing material" , "external sealing device" , "sandwich filling" .)