One of the few issues I have remaining with the MS/Asobo P-51D is that the hydraulic T-handle animation vs. function is reversed from reality. On the real aircraft, when the T-handle is pushed 'in', the hydraulic system is "activated", meaning that the hydraulic system will become pressurized off the running engine, and then when you pull the T-handle 'out', it releases the hydraulic pressure. In the MS/Asobo model, the T-handle animation/function is backwards. Also, unfortunately on the MS/Asobo P-51D, the inner landing gear doors drop down after shutting the engine down even without deactivating the hydraulic system, which isn't accurate.
On the real P-51D, while the landing gear itself is held up with mechanical up-locks, the inner landing gear doors (commonly referred to as the "clam shell doors"), are only held up by hydraulic pressure when the landing gear is down. Therefore on the real P-51D, if you don't release the hydraulic pressure via the T-handle after engine shut down, the hydraulic system remains pressurized and will only release pressure based on how air tight the hydraulic connections are. If the T-handle isn't pulled, the inner landing gear doors could remain in the up position indefinitely, or slowly lower over time as hydraulic pressure bleeds out of the system at any weak points. It is common practice, especially amongst modern operators, to pull the hydraulic T-handle after engine shut down so as to not keep the hydraulic system pressurized, and when doing so the inner landing gear doors will drop to their fully open position in a matter of a few seconds.
On the real aircraft too, if you pull the hydraulic T-handle, you won't be able to raise the flaps. I've seen a video on Youtube where a P-51 pilot at an airshow some years back forgot to push the T-handle 'in' prior to start (as normal checklist procedure), and so when the engine started the inner landing gear doors remained down. The pilot only noticed his error when he went to raise the flaps before taxiing and they wouldn't go up, so he immediately knew he'd forgotten to push the T-handle in. You could see by the video that as soon as he leaned forward in the cockpit to do so, both the landing gear doors and the wing flaps began to rise.