I think you guys might have an animation problem on the P-40. When you say you are pushing the hydraulic "button", I'm pretty sure that is the trigger for the guns. What -should- be animated is the hydraulic "toggle switch" which is the thing that looks like a bicycle brake. The pilot would operate it with his pinky and his ring finger. I've watched the video in question and I think it depicts that. Also, the training manual by Periscope Film LLC, page 25, shows that as well. No "thumb action" involved there.
DISCLAIMER: If I'm wrong about that, then I'm wrong, but you might want to double check because I would have sworn that was how it worked in one of the online training films.
The operation of the flaps, while on the ground in the P-51 that you demonstrated, got me thinking: Do you model Flap Droop and Flap Creep on the P-40
I think if you put the flap handle in the down position while on the ground that the flaps should droop on their own when the system is not
pressurized, on the P-40). Also, a checklist for the p-40 found at http://www.aerofiles.com/checklist-p40.html
says "Note: return landing gear and flap control levers to neutral after completion. The flaps will creep up if selector is not in neutral (positive lock)."
(okay, its back to Skyrim for BigJuicySpider