Black horizontal stripes in 75 mm interval

Recently, I got a Samsung ML-1640 Laser printer which produces black horizontal stripes which occur in a 75 mm interval. The 75 mm indicate that it might have to do with the drum which has around 24 mm in diameter.

This problem seems to occur frequently as my first ML-1640 which I got 1 year ago also had the very same problem. At the time I solved it by inserting a refilled drum-toner-cartridge from Ebay.

I would like to get it working again without cartridge replacement this time. Who has an idea what to look for specifically? The cartridge can be dissassembled to the last piece.