AFX Slot Car Light Wiring

There are lots of wiring experts on this forum so I though this would be a great place to ask.

I have a slot car that has a voltage regulator (see attached diagram/pictures) for the lights and I am struggling with the diodes. The regular diode went (the diodes seem to expire on these boards) and i replaced with a small schottky i had on hand (which was still too big than needed but fit under the cover). I was wondering if someone could help me out to spec the two diodes? the resistor in the diagram is a 1.5kohm @5%. While i recognize the circuit as a voltage regulator I don’t really understand what it is doing.

A second question, I have a number of cars that have a single light that I would like to convert to LED that have the same large input voltage range (5v to 24v). i was thinking i could use a small regulator like a 79L05 to give me a constant 5v then use a 3mm led. this should still be a fairly light package (weight wise) and draw less current than the tradition bulbs the manufacture puts in the car. I would use two resistors, one to limit the voltage to the regulator (as it specs out at a max of 20v) and a second resister to put inline with the LED. 100ohm 1/4w should work in both cases. Would this work?

the car with the regulator in it is extremely slow so I may look at replacing the regulator they have with something small and LED to make the car faster and a bit more competitive.

any ideas would be great, thanks!

the zener looks like it has the number 6 (or if you squint, it could be a 5) on it? i can't find any references to what that may mean though.