Which pokemon should I replace? Pokemon black help.?

So far in pokemon black I'm about to go up against the elite four. So all my pokemon are lvl 40~50 ish. Currently on my team are:

Jellicent(44)

Scrafty(50)

Serperior(42)

Fraxure(41)

Darmanitan(43)

Eelektrik(41)

I want to add in a Rufflet/Braviary into my team. I'm thinking of replacing Serperior since it hasn't really been helpful unless its against Water/Ground types, and Darmanitan as well, though his performance was more satisfactory than Serperior's. The reason why Scrafty's level is so high compared to the others is because I decided to level him up ahead of everyone else to beat the 8th gym leader since at the time Fraxure still hadn't evolved yet, and was quite weak. Jellicent and Eelektrik are also crossing my mind since they're not really taking hit wells at the moment (especially Eelektrik, though I expect that to change when I evolve him sooner or later). I'm regretting not starting with Oshawott since Samurott seems the better choice over Jellicent and Serperior, but well yeah. So any suggestions?

Who should I replace and why? Thanks for the help in advance!