T10 LED lights

There are plenty of LED versions of the 194/168 Lamp available. Check your preferred auto parts store. Sylvania makes one with a bulb-shaped plastic top that gives a fairly good result.

Edit: Generally, the landscaping lights mentioned below are too bright. You do not want to replace a 5W equivalent lamp with a 20W equivalent.

As it happens, a couple of days ago I googled "low voltage wedge base led bulbs" (looking for some LED wedge base bulbs for my garden lighting) and a lot of different sizes popped up, including T10.  The one thing to be aware of is how the LED 'bulb' is built.  Some of them have one or more SMD's mounted to provide light out of the 'top' while others have four SMD's arranged to provide light out of the sides (i.e., 90 deg apart).  Some of those also have a fifth SMD that shines light out of the top.  I don't know how the socket is oriented in the caboose - probably worth checking out and then finding the right LED arrangement in the bulb.

Led light can also be labeld wide or narrow in focus. Go wide mostly.

LED do not like over voltage and will cook in an instant (the automotive ones should be good to about 14-15v)

They are dc devices. You need a regular diode on either wire for use on ac track with most led. And maybe a resistor to keep it under volt limits and/ or dim it.(variety pack to dial them in 10-500ohm, then buy whatever.  Supposed AC safe led? Counts on a breakdown voltage of the led sometimes, I suspect a shorter life that way and would spring for the regulator diode (dirt cheap, general purpose rectifying diode)   A bulb will still work with a diode in place too. Some led may actually have a regulator diode already in the base.

Once you do it once or twice, it will be easy