Front fan spinning but cooling is suddenly poor, issue started again 3 weeks after swapping in a new front fan  

Front fan spinning but cooling is suddenly poor, issue started again 3 weeks after swapping in a new front fan

Hi all, been having a problem with a MK3s+ i got at the end of march this year

Its on its 4th part cooling fan! after about a month the cooling seems to start getting poor and gets worse as time goes on. the fan is always spinning, set to 255 and passes self test, it doesnt seem to be spinning slowly compared to the other printers but its hard to see clearly.

Issues I am seeing on prints, saggy bridges, saggy solid layers over infil (top layers), sags on Gyroid infill when crossing from vertical to horizontal lines & support is harder to remove from prints.

Whenever I swap in a new fan I have checked the wires and they are fine. This is one of 3 Mk3s I have here and I dont get this issue on the others (so I think it is not environmental). New fans run fine for a while then all of a sudden start degrading and get worse.

I clean the fans by holding the middle section so it cant spin and use compressed air to blow out any dust, there is nothing blocking the fan duct or shroud, there is rarely any dust there as the printers arent in a dusty location.

I have contacted Prusa but they want me to send them my einsy and this is a production printer which I really cant afford to lose at the moment, reaching out to see if anyone has encountered this issue. I have looked at the connector for the front fan on the einsy and it appears to be fine and securely connected to the board.