Re: the balky e-unit. I have one of these, and it also had this problem. I found that the drum did not rotate easily, which meant a higher than intended voltage was needed to cycle it, because the finger contacts were putting too much pressure on the drum. I just bent them back a little, until the drum was loose enough to move at 6 volts. Didn't even have to take the e-unit apart. There was still enough pressure on the drum for good electrical contact.
Other things to look for might be a burr on the inside of the holes which support the ends of the drum, or the side plates of the e-unit being pressed too tightly together.
That being said, adding diodes to slow the motor has the advantage of increasing the minimum operating voltage, which improves the smoke output and headlight brightness when running at yard speeds. So that approach has something to be said for it.
I often run mine using a PowerMaster. Not only do I get to follow the switcher around, but the jagged waveform seems to effectively increase the voltage seen by the smoke unit and lights. The motor and e-unit are louder when run this way, but not offensively so.
Also, I made a mod to the smoke unit which was recommended at the time. That involved drilling an 1/8" hole through the interior vertical partition, right at the center of the resistor (in these, the resistor is mounted vertically, and surrounded by a fiberglass sleeve, which wicks the fluid up to it). That took smoke output from non-existent to actually pretty good (for that era, anyway).
