I have said for a long time that there is no such thing as a cheap old airplane. A 172 that old has numerous parts that are nearly impossible to get because they have been out of production for a long time, and there are no aftermarket sources. The owners of such airplanes tend to clean out the salvage yards to keep their own airplanes going.
The main gear legs are a good example of rare parts. Those old spring-steel leaves are cut from spring steel, the edges carefully radiused, holes are drilled, the leg bent to shape, the bottom side shot-peened to create a dense, hard layer, and then the whole thing is heat treated. Hardened and tempered to very precise temperatures and quenching.
But that high-carbon steel corrodes. Corrosion causes pits in it, and on that bottom side, which is in terrific tension every time the weight of the airplane comes on it, is compromised. Because it is so hard, it can crack and fail suddenly, and some have done so. That tends to total the whole airplane. The worst spot is under the entry step that is clamped to the leg; moisture gathers under that area and causes rusting and pitting. Cessna has a bunch of service manual revisions on this. The pitting can be dressed out if it's within certain limits of depth, but if the dressing has to go too deep, re-shot-peening and heat-treating is now necessary.
Not cheap. And used legs from a wrecker are likely to be similarly affected.
Some more commonly-replaced parts are available from MacFarlane Aviation, Stene Aviation, Dynamic Propeller, and others. An outfit in Alaska make engine cooling baffles, but a good mechanic can also create those.
