Just got my first Walther ppk/s, very impressed with the quality of workmanship. It is a .380 in nickel finish, the last two numbers of the serial number are 77. Question, is this the year of manufacture, it is a West German model imported by Interarms, how rare was the nickel plated model, this is in brand new condition with box and manual, any ideas how much it is worth. Thanks in advance.....