With these old bike sooner or later you'll probably need that whole catalog
There may be some oil seeping somewhere also , I can't tell with the pics , but I know with mine that leaking gas turn oil colored and viscocity wise from dissolving dirt and grime buildup plus evaporating some so it can look like oil , but the smell of any droplets should tell you which it is. Oil in the airbox may be from the breather hose that is attached to the front of airbox between the 2 intake boots right behind the shock. Technically it can be unplugged right there and put a breather filter on it so any oil vapors go to atmosphere rather than in the airbox . Plug the nipple on the airbox where it was plugged into though.
First we'll start with the carb .
The Kedo catalog isn't in english very good so I'll post another page to hopefully show what you'll need ,
I don't know which year your XT is but this should cover yours
http://www.partzilla.com/parts/searc...TOR/parts.html
Parts that should be replaced are ,
#22 & #21 = drain screw and o-ring , they are generally pretty beat up so just get new
#16 (maybe #25) = pilot(idle)mixture screw ,may come as a set so #25 isn't needed , not sure how they come.
#10 =needle valve set , will have a small filter and o-ring
#56 = secondary carb main jet o-ring
#17 = float bowl gasket , I'm not impressed with the ones I get from partzilla , I don't think they truely are Yamaha seals , they're rather thin and barely seal plus leak in a few months usually, can't reuse ever without leaks. They get hard quick thus leak, maybe Kedo has better quality ones.
#6 = primary carb mainjet o-ring
#39 = fuel line between the 2 carbs ,mine have been hard and leaky , you can just use 6mm fuel lines and better clamps.
From your first picture it looks like some leaking is coming from up high , can you take a few more showing the tops af the carb and different angles?
If you start getting into disassembling I can help with pictures of my own so you can verify its done right. Once you learn it's nice not having to pay someone else.