Before you spend money, I'd remove the cap and see if it still runs.
Here's the Lionel search on any RCM2 boards: https://www.lionelsupport.com/...;submitButton=Search
I'd probably use the Trackmobile one and install my own cap. Pick a 35V one, the largest that will fit in that cavity. I'm sure the 2200uf isn't super critical, so I'd just use the dimensions and find what will fit with a suitable rating.