I considered the AP but the Diver and just missed out on one, what to look for buy as new as you can try to make sure it's in warranty if buying from an AD, service cost's for older Jumbo's can leave you with a large hole in your wallet, make sure it has provenance the 39mm has been replaced with a 41mm check them both out, this baby has been around since 1972 and i think there could be part's issues with older ones.
Any service cost on the AP is eye watering, and 2K is not unheard of.
Make sure the bezel has not been over polished and rounded, AP will only polish 3 times then replace, it can not be polished anymore as the screws pose a problem.
Other than that enjoy.