A reversible belt lets me look perfectly natty, regardless of whether I’m wearing my brown pants or my khaki pants. The post joining the buckle and the base worked loose, so the spring wasn’t holding the two parts together; obviously, something must be done.
Loosen the four screws that hold the leather belt in place to reveal what’s inside:

Then push the two parts together and give the post a few shots with a sharp punch:

Reassemble in reverse order: done!