Removing old hard putty

plumb1_2

Quincy wrote:

Er but what happens if up a ladder they are quite heavy, plus I cant see how a router would get in the reveal of the window opener, I think its quite hard to do. (ex Glazier)

Not all routers/cutters are heavy see here just put a straight cut blade in, pin a piece of timber(1/8"x1/2") on the frame to act as a guide.
Set the plunger to just short of the glass, rake-out, tap out glass, the reset the plunger to clean out the rebate. Simple.