The ceiling fan is over 30 years old worked flawlessly until now, light either blinks or shuts off altogether. But, when you turn the wall switch off then back on it lights up no problem for days, then back to it. Also, the wall switch has been replaced thinking it was the culprit, but to no avail... This fan is in my elderly mother's home, which she will be 90 in Dec. But the fan is in the kitchen above the table ...
Filament a likely culprit, but is the fan perfectly balanced? We all assume not perfectly. Bad connections, even good ones, break with enough movement over time. Potential chain of events:
Power on - rush of power bridges air gap, or gap doesn't exist, connection holds together
Running - something gets hot or vibrates loose, loses connection
Stop - cooling or lack of vibration allows physical gap to close enough so that...
Power on - rush of power bridges air gap, connection holds together, repeat
The connection could be filament to post, switch to wiring, internal in the fan, the place where a rat ate away connection material, anywhere in the current loop really, but filament, switch, and internal to fan are my top three suspects.
On old fixtures I have found the center contact to be the problem many times. With the power off remove the lamp, use a small screwdriver to lift the center contact about 1/8" replace lamp and see if that fixes it. If lifting the center contact fails next I would be looking at the wiring on the fan, the switches used in fans even old ones are usually quite cheap and can fail as a loose connection also. I would check the socket first as this is quick & easy and has solved a large number of light fixture problems for me in the past.