Good Morning Elisabeth........Sounds like the crop is probably overstretched because it takes so long for last 2 cc's/ml to empty. Maybe you could fashion a crop bra like Yeuda has for his Rose? Otherwise it means (as you know) emptying that crop once a day at least, better more than once IME though. I would put a small drop of the warmed Nystatin into the crop, after you empty it next time, BEFORE you add any formula (I would do that everyday). IF you see or suspect yeast at all then I would add some to the formula also.
I would suggest you throw away any syringe you may be currently using and use a new one. I store mine in the freezer immediately after I rinse it out well, along with my S.S. gavage metal feeding instrument. To be on the safe side I would purchase asap some new formula (Kaytee for Baby Birds) if ya can get it. If ya have to continue using the same formula that you already have, smell it, one can usually smell if it is bad or rancid IME.
Well, if ya rip or tear the lining of the esophagus the food can get between the lining and the crop wall and an infection will occur and the baby will most likely die so watch closely the crop wall and make sure you don't see it being pinched or sucked into the tube you are using. Actually you should also be flushing the crop with warm LRS after evacuating it BUT very dangerous if ya aren't extremely careful so maybe best to just get out all ya possibly can and add the Nystatin if you don't see any obvious signs of yeast. It is kinda tricky to hold a struggling Tiel while stretching the neck properly and inserting the tube by ones-self. However, if you have no one at home to help you and if you have no qualified outside assistance, then ya have to do your best to do what needs to be done to save a life.....I find it a lil easier to put the formula in a glass shallow dessert like cup and add room temp. water to it while mixing and then setting vessel into a pot of water on the stove that has just been reduced from boiling. I continue to mix formula with spoon as the vessel sits there until the proper/desired consistency. Just seems easier to mix that way and formula doesn't get over-cooked as easily IME.....I wouldn't be too concerned about getting the temp. of formula perfect, as long as it feels slightly warm to you on the underside of your wrist, that should be fine for a baby his age. (Just be positive not hot enough to burn).
If you have a vet supply warehouse in your town by any chance, you can probably find the S.S. gavage instruments there or you might want to order on line to have on hand in the future for any needed feeding or medicating emergencies/procedures. You would want to order a #14 & a #12 for tiels and I even suggest a #16 for the new hatchlings in an emergency.
Anyway, sounds like you are doing great, the lil guy should make it.
Thanks for answering the questions asked in detail and thanks in advance for posting the pics later when ya can, may possibly help some? :)