Unfortunately with the current verisons of Electrum, you cannot import private keys into Electrum, only sweep. This is fair enough, because the addresses would not have their private keys saved along with your backup seed anyways.

The best option is to create a brand new Electrum wallet using your 18 words. I've PM'd you if you need help doing this. The easy way out is to simply send your Bitcoins over, rather than migrating. This works if you don't care about the addresses you previously used.