Got a 1928 Jhonson A-35 that hasn’t run for 50 years, now purrs like a kitten. the brass petcock leaks, took it apart and looks like it has had sand in it. can I polish inside mating surfaces with lapping compound or something like it? Member of Puget Sounders chapter at 73 years old I am still new to outboard repair. any help would be greatly appreciated. thanks again