iPod A1136 will not turn on normally, must be reset each session

iPod 5th generation (video), model A1136, 30 Gb

Problem: The unit will not turn on "normally", i.e. by pressing any button as described in the manual. It resets reliably (menu + select buttons held for several seconds) and continues to function correctly, including playing music, connecting to a PC, interacting with iTunes, and going to sleep. The only other problem with the device is a broken Hold switch (plastic tabs sheared off), which has been manually switched to "unlock".

The reset procedure has supplanted simply turning it on; this is a minor inconvenience, but perhaps a unique firmware error indicating an impending hard drive crash.

Backstory: This unit had a battery replaced by Apple 3 years ago, then failed shortly afterward (no operation and gave "Please Wait. Very Low Battery." warning each time it was connected to a PC) and was shelved. I recently disassembled it and found the battery connector was loose and the Hold switch actuator tabs were broken. The switch has not yet been replaced, but is set to "unlock" and otherwise seems fine. The insides were air-dusted clean and everything reassembled. The unit was Restored using updated iTunes software, charged overnight, and some music was successfully loaded. All other functions are normal.

Thanks in advance for any advice. I am grateful I found your site, it gave me the information and confidence to open up this unit and perform the initial repairs.