I have several GE machines and this gross mold is a too familiar. It also forms on some of the hardware on the Roll-Easy, like the bag chamber latch mechanism, and on the exhaust port cover on the pink Roll-Around. I'd be interested to find out exactly what kind of mold it is, and why it grows specifically on these 50s GE-made Lexan parts.
Like you've already discovered, bleach is your friend. I've found it useful to soak difficult cases in a bucket of hot water mixed with ample bleach. It then turns to slime and wipes off. You may need to flake some of the heavy deposits off after soaking to get them completely spotless. You also may want to take apart that pink floor tool, as there will be mold inside as well.