Another thing good to know is that some of the late-80s early 90s bikes were made by people pushing the envelope of steel technology. This means it's especially crucial to inspect before you buy if you decide to purchase.

MB-zips and P-23/P-22s were prone to dents, cracks and weld/braze pops. Some of those bikes have been repaired once or twice - and given that the steel had to be heat-treated for full-strength, one has to often wonder whether the repairs were done correctly.

This is true for all 6061 aluminum bikes as well. They lose some strength if one does not heat-treat after welding.