1) Panerai doesn't "repair" PVD cases because stripping the PVD and then re-PVD'ing is a huge pain in the butt, so they simply replace the entire case.
2) Never used any so can't recommend. Plus, mentioning any 3rd parties is against our non-commercial guidelines, so if anyone has recommendations, please send only by PM.
3) Nope. Keep original as possible.
Cheers,
Anthony