I've had the 'filmy screen' causing a big fogging problem a couple of times, most recently on Rattiva II. Gawd knows what was on there but it took industrial strength solvent to shift it
Since then things have been much better. It also helps that the heater works properly but that's another story...
Sadly, the corroded calipers are an all to common problem here. Basically, you need to get the calipers off, chisel off the corrosion and refit but the devil, as always, is in the detail.
The two through-bolts that secure the calipers to the trailing arm are high-tensile and love to snap. You need to exercise a special method of extraction as follows:
Wire brush the ends of the threads where they poke through the trailing arm and douse in Plus Gas (not WD40) Wait for it to soak in.
Use a 17mm socket on the end of a long breaker bar and use gentle but sustained force to just move the bolt. It will feel springy at first and this is the dangerous time. It's initially springy and then snap!
So what you must do is to only move the bolt a little each way initially. Undo just a tad, do up just a tad and repeat as you slowly undo and do up a little more each time. Don't rush the job and take it very carefully and slowly. And don't try to undo the bolts quickly just do it in very gentle stages.
The secret to having none shear on you is to have a set of spares on hand (Part No. 96 172 064 for the hatch) at a cost of £16.
If one snaps then the only way to see it out is to weld a nut on the stub of the thread poking out. It is far too hard to drill.
Once the calipers are off, remembering to replace the small 8mm through-bolt to hold the two halves of the caliper together, use a sharp cold chisel to remove the corrosion. Wire brushing or sandpapering won't touch it. Then reassemble with plenty of copper grease on the faces to stop it happening again for some time.
After that a new heater matrix is dead easy!