I've been using postwar ZWs since 1950, and when MTH came along, the ZWs have presented no problem and one of them is still powering a portion of my layout. Your problem must lie elsewhere.
I also have a #624, and over the 65 years I've owned it, it has been the test bed for some very unusual control systems that I had designed, one of which appeared in OGR some 30+/- years ago. Most recently, I converted it to PS2 and it runs quite happily. I must confess it doesn't get used too often because the Magne Traction is weaker than it was about 1953.
