Overhead light does not stay on

FYI.

Had an overhead fixture that suddenly started turning itself off. Thought it was the bulb, so replaced and it came on - a few minutes later it was off again.

Took the stitch apart - NOT the switch.

Took the overhead fixture loose from the mounting box, but did not undo the wiring. There was a buildup of debris on top of the wires and on one side of the porcelin.

Cleaned off the debris - light worked correctly. Reattached to the box.

Building is over 25YO and I'm sure noone had ever removed the fixture (could tell by the paint color under it).