sticky substance almost always indicates scale; and there it is on the underside of the leaf in the first photo. There is a lot of information on this site as to how to treat scale, if you do a search. BTW there are probably a thousand or more types of scale; they are spread by birds, some insects, and even by the wind; so you have to be constantly vigilant.

Yep, scale. Like John said there are lots of posts that talk about how to get rid of it. What worked for me was manually removing and crushing all scale then washing the leaves with the hose sprayer rubbing each leaf to get the stickiness and gunk/eggs off paying extra attention to the underside of the leaf. Then I sprayed the tree down with a mixture of Horticultural oil, Neem and Protek. I did this weekly and about 4 weeks was how long it took to eradicated though I had a smaller infestation than you so it might take a bit longer. They are small and easy to miss especially on branches and the trunk so be as thorough as you can.

Sammers do you mix this or spray alternate> No clue what protek is. Have to look it up

I mix, mostly because I have both at my disposal and Protect is a DynaGro Silicone product that I uses as the emulsifier/sticker. It is recommenced on their bottle of Neem instead of soap as some people use. I think Insecticidal soap is supposed to work too, tbh I think the manual removal and washing of the leaves does the most work.

Sticky stuff also may indicate mealybugs, whiteflies, and/or aphids.

A number of aphids, both big & small, are obvious in the 2nd image.