Paradoxically, what one may do to gain a seat? (5)
I believe the answer is:
stand
'what one may do to gain a seat?' is the definition.
(as in standing to win a seat in parliament)
I don't understand the remainder of the clue.
(Other definitions for stand that I've seen before include "Be likely to rise" , "Base < put up with" , "Tolerate - resistance" , "Be upright; attitude" , "stick" .)