If all the seals in the entire system are shot, odds are it wasn't a place that just topped up the level. The brake system doesn't flow, it only pushes back and forth, so for a bad fluid to make it to the discs/pistons, the entire system would have to be filled with the bad fluid (meaning it was done during a full system bleed or flushing). Topping up with bad fluid will usually only damage the system near the reservoir (ie master cylinder), but can still have severe consequences.
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