Where do 914s rust?

The worst places are the main structures along the sides of the car, the longitudinal beams, or "longs". These run from the front wheel well back to the rear suspension mounts. The most vulnerable spot is beneath the battery on the passenger side of the engine compartment. Batteries leak acid, which mixes with water, dirt, leaves, and other cruft to eat away at the section just forward of the battery down by the firewall, called the "hell hole". ANY rust here is a problem, even if it looks like it's only on the surface. Prodding at this with a sharp object like a Phillips screwdriver is very important. The rear suspension mount just below the battery also needs to be checked, along with the section behind the valance along the side, below the door.

The jack posts frequently rust out, often eating into the long, too.

Any rust-through on the longs would be grounds to walk away from a potential purchase. Fixing this is possible, but requires a great deal of work and much welding.

If everything LOOKS OK, here, then try this simple test: open the passenger door, and close it gently. It should close with a nice click. If it takes effort to close it, look carefully at the gap between the door and the rear fender. If it's tight at the top and/or loose at the bottom, the car is sagging in the center from a badly rotted long. Repeat this test, only with you sitting in the passenger seat.

The rear trunk floor often rusts near the taillights, usually from bad seals.

The front trunk is often covered with surface rust, which isn't a huge problem.

The floors can rust under the undercoating often applied to the outside, and the soundproofing applied to the inside. In bad cases, this may extend into the crossmember or center tunnel. You often see rust under the rear window on the inside (behind the backpad) caused by a leaky rear window seal. The section where the floor meets the back wall of the cabin is a great place for rust to form. Most of the floors are not structural, so it's not too critical as long as it hasn't also spread into the back wall or the crossmember or tunnel.

On those cars with vinyl on the targa bar, you frequently get rust under the vinyl, most often where the chrome trip clips to the body. The chrome trim around the windscreen is also a prime rust point.

Finally, bubbling paint at the base of the windscreen pillars is not uncommon, as well as around the inner lip of the front trunk, where the seal goes.