After 2-3 weeks of fighting to get Ruby going (unsuccessful) - I had the brilliant idea to buy an unassembled Heisler (yes, I'm that dumb). Neither train runs correctly.
Sorry to hear of your problems. I threw in the towel on my Ruby/FWRR loco after fighting it for years - it sits on the glass cabinet as a static exhibit these days.
However, the Regner Heisler is a different beast. Mine runs beautifully without any special build problems. The only issue we found was setting the reversing valve properly. Did you use the UK-English instructions from Graham at Gardenrailways.co.uk? Or did you work with the german?
The thread on MLS has most of the queries/problems and the solutions. Your YT video shows you need to adjust the reverser as we did!
I posted a similar thread on LSC.