Agree wholeheartedly with what rlepecha has said above. T Cut is very abrasive, so if you're trying to preserve, rather than remove paint, I would stop using it. A modern polish will do a similar job to T Cut, but is much more controlled.
What effects are you trying to achieve?
If it is a patina preservation exercise, I would probably not be too fussed with the polishing stage, and would instead concentrate on keeping a good layer of wax topped up on it regularly. Polishing is more regularly used in combination with claying to get a mirror-like finish, and then sealed in with wax. If your paintwork was more perfect like a modern car, then this is a great process for removing swirl marks and small imperfections. For a bus with old paint and wearing years of battle scars, you may not notice much difference by claying and polishing, but every time you do it, you'll be rubbing ever closer to the primer layer, which, as you say, you're already starting to see. Compared to a modern wax, Ankor wax is a primitive wax with positives and negatives. It is easy to put on a thick, protective layer that is hard-wearing, but it is hard work to buff off (if you don't want to leave a brown layer of it on your van) and everything sticks to it in the summer when it'll go tacky. I have a big container of it, but tend to use it in areas such as underneath rubber seals or trim where water might sit. Also, it's good for dabbing on 'rusty patina' but I personally wouldn't cover entire panels with it for the reasons above.
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