[Arran]

Joseph;
I'm happy to hear that you have also had some success with the vinegar wad method. I guess that cleaning vinegar comes in different strengths, the stuff I found at Canadian Tire was 10% Acetic acid, or 30% if you wanted a more concentrated version. The regular kind is only 5% same as what you encountered, I think I got it to work mostly because the rust wasn't quite as heavy, that or it I left the paper wads on longer. I thing that vinegar is the way to go, it's inexpensive, and it's safe, muriatic acid is basically HCl and whilst it will strip rust off quickly it will also cause it to reappear, it's also really hard on aluminum, and will destroy some plastics. I suppose you could dilute it, but then again vinegar doesn't involve the same handling hazards. If you want to stop the rust coming back phosphoric acid works as a rust inhibiter, some hardware stores sell it as a cleaning product to remove lime scale from water filters and plumbing, it's one of the ingredients in Navel Jelly, but it doesn't really work that well by itself as a rust remover.
I can see the issue with getting one of the end bells off of the transformer, it's funny because many transformers of that style just have the bells go all the way down to the chassis without the hole.
Regards
Arran