Hi Northwind, thank you for your quick and kind answer.
For third question, I don't understand why you find easier to swap heads (even more with this model, with this F.... magnet) than to swap 1 lonely platter. Is there something difficult in swapping 1 platter when heads are parked outside ? I never tried, but I can't imagine it's harder… only 1 screw and a PCB to Xchange…
EDIT : While writtinig, I was thinking and understand that parking-plastic-piece is involved in platter swap because of it's position. So, if I understand, I should put heads over the platter, remove parking-piece (what's the good word for that ?), put heads outside, removing platter, changing platter, moving heads over, put parking piece in place, put heads again in park… and pray… that's it ? It's harder than just one screw and one platter… but it seems quite easier than head swap for this model, no ?
EDIT2 after writting : wouldn't be possible to let heads in parking place and just pull the piece 1 or 2 mm back to relesae platter ?
EDIT3 after trying : Forget edit2.