It's a long time sonce I've been described as Cundy the younger. My father lets on that I may even be older than you
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This is what I wrote about rust:
"Where to look for or to expect rust
Areas on the outer skin of the shell will be readily apparent (wings, sills, rear sub-frame mounts, front and back lower wings) but areas covered by trim or easily “bodged” will not be so apparent. I would advise to look (or expect to find) for rust in the following areas:
Bottom of rear panel – this is easily hidden by filler and fibreglass and is easier to see or feel by running your fingers around the inner seam inside the boot. It should be smooth and follow the natural contour of the panel. Any lumps or unnatural contours will probably suggest filler of some sort. Unless very localised this will require the replacement of this panel.
Inner B pillar channel. This is covered by trim and cannot be seen but it collects water from the rear ¾ window and rusts from the bottom upwards. If bad it can be felt by pinching hard through the trim – you will feel it give. This is a very complicated doubled skin structure and is not easily repaired. I would suggest (and I am doing) using bits cut out from a donor car and replacing the bottom three inches with this.
Back of ¾ window aperture. Where this meets the C pillar at the bottom I have often found small pin holes from local corrosion. These I will weld up locally. The are difficult to see as they are covered by trim strips.
Inner A pillar. The point at which the A pillar joins the front bulkhead (and upper valance) at the bottom corners of the windscreen are vital to the structural integrity of the whole car. Hidden by trim it can be felt by pinching through the trim. Again it is a very complicated structure that is difficult to repair, and is better replaced by a section from a donor car.
Rear window bottom frame. This is hidden by the window itself and the rubber trim. It is of a shape (convex with a backward slant) specifically designed to trap water in the corners and at the centre, and then rust! If bad it may be possible to see it by lifting the trim with a credit card and looking under. Alternatively it may be possible to see by looking from the inside, pulling back the trim. If not too advanced local repairs are possible but in advance cases (like mine!) the solution is to cut the old bottom frame out and fabricate a replacement. Note if this is rusty water drips into the box section underneath which causes more problems.
All suspension pick up points must be checked, two at the back and three at the front on each side.
Rust in the floor pans, inner sills and cross members should be readily identifiable be lifting the carpets and inspecting inside and getting underneath with a light.
The underside of all the subframe arms should be inspected from underneath.
Check inside the front wheel arches – where the brake pipe bracket is you can see a diagonal weld about 4 inches long. This is a poor design and I have never seen one on an un-restored car which is not split. It is the failure of this weld which I believe contributes to the wings cracking at the top. Most people say this is caused by the failure of the rear subframe mount system, but I think this is equally to blame. It can be welded up, but the correct solution is to grind the weld off and put a plate over both sides of the joint (inner wing and inner engine bay) and seem weld around it.
There will be other areas I am sure but this is a summary of what I have found in the course of my Fanalone, two previous Fulvia’s and my brothers full (no outer panels !) restoration."
Just from our experience so if anyone wants to add or contradict then please do.
I did help strip an S3 once - my only thoughts were that it was mechanically the same but FIAT accountants had done a Value Adding exercise (I can feel all the engineers shuddering as I write !) and changed many of the fixings from enginering cap head to DIY hex head, and there were plenty of choice words as we rounded heads and freed off siezed threads.
The wiper system is better than on S1 cars with two speed wipers and electric wipers. Regarding the light switches I think the trick is to make sure the a) nothing is broken and the contacts are clean(rather obvious !) and b) all the little set screws in the switch are done up tight - otherwise you will be treated to a light show thet Jean Michel Jarre would be happy with when you go over the first bump!
I think S3's are the best value coupes because they are the same as S2's just with a different interior which may or not be to everyones taste.
There are some differences to the head and valves (again part of the VA exercise I guess), but I don't think they are significant today.