I do this once a year:
Starting with warm soap water (Ajax) and a micro fiber (no scratch type) cloth, gently washing all fingerprints, dust etc. off.
Next I wash them with hot water, and immediately after dry them with a towel. I only do one side at a time, that's 9 times per Penta, to ensure that I remove all marks from the water.
Next I apply a thin layer of virgin coconut oil, which I have melted in a cup on top of a table lamp. I do this with a paper towel.
Finishing of by polishing them with paper towels to remove most of the coconut oil, leaving only a very thin layer.
Living room: BV7-40 mkIV + V8000, BL5, BL3, BM1 and BS9000. Bedroom: MX3000 and BL4500 on MCL2-AV. Around: PentaIII, CX100 and MCX35 on ML/MCL + MCL2-A, BeoPort and BL4 on ML, BS3300 + M75 as stand alone, BC6000 + BC600 and BT1100, LC1, LC2, Beo4, Beo5 and BL1000, BS2 and A8, EarSet2, Apron, Coffee mugs, Enamel Bagdes, Bath towel, Keyring, Books, Lots of miniature and the Bottle opener. Office: BC2300 + BL2500 and BS3. Summer house: BS Century.
Addicted? Oh no.... ;)