Help my Lemon tree!! 😭 Extreme Chlorosis

I’ve had this lemon tree for years now but in last few months it’s been appearing very sick and yellow, I have 2 oranges growing nearby that are doing just fine but this lemon tree has always been yellower than every other citrus I have. A few weeks back I gave it some urea (carefully measured amount) because I suspected nitrogen deficiency and applied Yates foliar trace element spray (looks like a nutrition issue?). However it’s actually gotten worse … Now the younger growth and leaves on the outside of the canopy are yellow, with some small shoots losing all their leaves with “black” ends and signs of curling up (image 4). The leaves inside the canopy still look healthy for now, I don’t think it’s disease related more like a nutrient or some other problem..

Does anyone have any advice on how I can help the lemon tree? That would be much appreciated, it bears very good fruit and I don’t want it do die. 🥲

Sorry photos are a bit dull because I took them when I got home yesterday in the evening