Only replace

Have U-shape knife with 24 mm and 36 mm blade lengths (sourcing reference: BMW Parts Department) ready.

Fit respective knife with required blade length:

24 mm = All round on rear window

36 mm = Recut window edges at bottom left and right

Fig 1: Identifying U-Shape Knife

Courtesy of BMW OF NORTH AMERICA, INC.

Regrind blade with a grinding stone while machine is running (new blades also).

Insert knife carefully between tailgate and rear window.

Guide web of knife parallel to rear window.

Cut through adhesive bead as closely as possible to rear window.

Lift out rear window.

Pull off adhesive tapes all round.