Bipolar ones where they are will continue to work properly but those two that are not may be reverse biased or not biased at all and eventually stop working.

Yes, I think similarly. I thought about a complete capacitor replacement and noticed that so a lot of bipolar capacitors are installed. According to the service manual, there should only be two, but exactly this two that should be bipolar are polarized. Strangely enough, the sound sounds ok. I will definitely fix the problem on my card. I want to document the problem here on the forum, as I haven't found any mention of it anywhere else, and it's apparently a manufacturing defect.