In 1990, a Philippine Airlines Boeing 737-3Y0 was waiting for takeoff from Manila when the center fuel tank exploded.
In 2001, a Thai Airways International 737-4D7 was destroyed while sitting at the terminal in Bangkok. The aircraft was being prepared for a flight when it exploded. A bomb was suspected at first because initial tests showed traces of C-4. Later tests by both the Thai military and U.S. investigators did not find any traces of C-4. (It would have been good for the Thai government for it to have been a bomb so they could have used it as an excuse to go after the groups who were at first suspected of the "bombing".)
The design of the center fuel tank system on the Boeing 737 and 747 are very similar. (This may have been changed on the newest models but we're talking about the 737/747 Classics [747-100/200/300 and 737-100/200/300/400/500 series].) A problem with one type would guarantee both require modifications.