The replacement 4 mm Polycarbonate windows arrived yesterday - I'd ordered them cut to size. So I started removing the old ones. With the windows removed I was able to get at swarf that previously had been inaccessible.
It was apparent that last time some of the holes were marginally too tight a tolerance with the screw thread binding on the polycarbonate - this probably contributed to the cracking.
I used the old windows as a drilling jig to locate the new holes - some were too broken so the new polycarbonate had to be temporarily installed using what holes that I could locate, then drilling through the holes in the frame of the machine located the rest.
The 'plan' was to enlarge the 6 mm holes thus produced, to 10 mm with a step drill, insert a 6 MM i/d 8 mm o/d nylon bush into the 10 mm hole, and tighten the bolts onto the shoulder of the bush allowing just a small bit of 'float' for the window by means of the 8 mm / 10 mm of the bush and hole. The bush projection 'shoulder' is bang on 4 mm and the sheets measure 3.95 mm.
I'd hoped to re-use the original 12 mm bolts but they proved just too short now the bush was there, for the shakeproof nuts plastic insert to engage, so I suspended operations until an order for some 16 mm ones arrived this morning.
All went well, and the bolts were tightened down to 'no play' then backed off a 1/4 turn. So hopefully there are no great stress risers in the windows and they may just last a bit longer

So - old windows - cracks all over the place - chuck them out ? No way ! Trim them down using the circular saw and release the 'good bit' from the middle to add to the pile of 'may come in useful' bits
