SEj support is not viable.
I tested it many times and i tried your build for 3 games, i was completely zoned and useless (gold). It's a dislike for me

I've had a little bit of a break of League but am diving right back in.

Thank you for the advice and I will do some refinements to the guide!

I also like to play Sej as support and have done well in ranked with it, I only started playing recently and got into ranked in the S4 preseason, but I almost made my own guide for it because of the complete lack of support guides for her.

Did you mean Rylai's Crystal Scepter Twinkieishere17? Frozen Mallet gives AD and Sej is full AP.

I find that if I get Rylai's Crystal Scepter and Liandry's Torment I become a major threat as well as a tank (you don't even really need the Scepter as you are so full of cc anyway).

You need to update it my friend. :D This is a really nice guide but Sightstone might be outdated because of the trinkets like the Greater Stealth Totem, but that doesn't give health and you can't get it before level 9, so maybe it isn't. You might want to look into Frozen Mallet or Rod of Ages. Also you possibly forgot a slot on your core. I'm not sure whether that was meant to show that we should pick 2 of the optional items or not. If that is the case you might want to through in a notes bit saying so :D

Like I said this is a really nice guide, but with a little bit of updated it could be a great guide :D. Good Luck

Since I'm commenting I figured I'd point out some grammar errors :D the quotes are the typos.
In the Summoner section you misspelled useful as 'usual' in Ghost's description
Also 'kill potential' in Ignite's description