One of the first questions that comes to people's minds when they contemplate purchasing or restoring a Opel Manta A series is where do they tend to rust. The body panels are getting harder and harder to come by and items such as the aftermarket wings can take a lot of work to get fitted properly. If you can manage to get proper GM ones they cost a fortune.
These can be hard to repair and they do rust where the front cross member bolts on so pay good attention to these.
Since the car was assembled before painting, coverage on the inside of the valance was not very good. The cars tend to rust at the bottom of the headlight surround; this is best seen with the grill of, where the upper and lower valance joins this area rusts from the inside out.
These are easy to inspect the first area they tend to go in is where they bolt under the floor
The front outer wing is bolted to the inner wing the inner wing tends to rust near the light surrounds, as there was a drain hole there
There is a box section fitted to this panel and it continues onto the inner wing slightly, this box section tends to rust, one of the first signs of rust in this area is when you start to get a hole on the engine bay side of the car, to repair this the box section has to be removed and repaired/replaced and when its of the inner wing / bulkhead area can be patched.
At the top of the kick panel there is a joining strip this also rusts away
The kick panels in the bulkhead tend to rust where they join to the A post section. Also rust can normally be found where the outer wings bolts to the floor of the car.
Main problem with this area its hard to inspect with the wings on the car.
On most Mantas I have come across the floors have been fine apart from the front Jacking points, unless these have been replaced you will almost find this area needing work. There are always exception to the rule and if the car has been prone to water leaks the sponge on the floor will hold great amounts of water and the floor will rot away so make sure you are happy.
The floor area around here does not really give many problems although the petrol tanks always seem to rot at the top rear side.
What car does not rot in this area, easy to check this out, if it is really bad also check the inner sills, on early Mantas with no B post there will be a 3rd inner sill. The easiest way to check this is remove the rear side panel inside the car and put your hand down towards the sill, you should feel a solid panel with round holes in it just over an inch in diameter.
The lower rear valence is an enclosed area that is not waterproof so these do tend to rust and if you put your hand up behind the rear valance you should be able to tell if the metal is solid or not on the inside panel.
Battery boxes tend to be heavily rusted. Battery fluids leak causing rust, and the drain can clog allowing water to puddle in the box.
If a car sits in the rain, water can get into the doors and this can result in some rust through holes in the bottoms of the doors This can be observed by opening the doors and inspecting the bottom of the doors from underneath.
Inside the rear wheel arch to the front you will see the rear seat belt bolting bracket water does tend to get in behind this and over time it will fall of, this is easy to see if the rear seat is out you will see the rust from the inside. The rear wheel arch itself tends to rust as with most cars but a repair section can be got for this area.
At the back of the rear wheel arch towards the rear valance there is an outer and inner section these are sure rust areas, as well as the boot well.
Now it would have been easier to explain the non-rusty areas :)
My advice is when viewing one of these great cars is to get under it and spend loads of time inspecting it, or you could end up spending a fortune. Cosmetics can always be sorted easily; major bodywork takes up a year or two of your spare time. Good luck with the hunt