I have just seen this video after fixing my wf321p earlier with this exact fault. I have to ask though about how you have fitted the electrolytic capacitor on this board. I can see the polarity before you remove the faulty capacitor and the markings on the board are a white circle and a + which both show the opposite that you refer to as “positive on the left” as the +ve is clearly marked on the board to the right. The white band marked -ve on the capacitor can be seen before removal and is nearest the small 8 pin I.C. adjacent to the capacitor being replaced which is the white circle on the board. I have a photo of mine before removal which also shows this. Basically, it looks and sounds to me as though you are fitting this capacitor the wrong way round. The link below also shows the capacitor with the -ve side nearest the ‘chip’ and “on the left where the little white dot is”. Electrolytic capacitors fitted the wrong way round don’t usually last very long and can ‘go’ in style as it were.