STI levers are not as hard to work with, as one would imagine. BUT, the Dura Ace ones are quite different to the Ultegra and 105 and are more difficult (I have worked on them all, but only in 9-speed guise).
There are some interesting videos on Youtube, to help. If you have some knowledge of bike mechanics, take your time, and follow the videos, you might be able to fix it yourself. Just remember, to keep track of how to get back to the previous step where you were - if the next step seems impossible, stop and get a pro to help.
Good luck