In the words of Meatloaf you took the words right out of my mouth - not that I'd be kissing you Beaky.

I thought the bleed resistor was to keep the filament warm so it stood less of a chance of blowing when energised with the feed from the drive transistor, but this would also speed it up as it lights.  The reaction time of an incandescent globe is about 0.1 seconds.  By the way this is a very good reason to change your car brake lights to LEDs, the faster response time should lead to less chance of a rear ender.

Back to pins; The resistor doesn't seem to be present on all the incandescent flasher lamp circuits.  When I first got my Firepower it was not there and I blew a lot of 89 globes, so I stuck the bleed resistor in and the blown globe problem ceased. The resistor does run pretty warm so I stuck a 5W ceramic one in.  On my Gorgar which has a similar flasher there was no resistor and no excess globe blowing.

The schematic shows the resistor as a 330 Ohm, cold globes are about 3 ohms, ,more when they heat but roughly that would mean 80 mA flowing through the (non flashing) globe (28V / 330 Ohm).  If you stuck a LED in (the sums change slightly, maybe 28-5/330 = 70mA ) but this would be enough to get the LED to glow.

In practice, if you have the resistor in the circuit and stick a LED in and it glows then remove the resistor.