Lightweight construction? You mean people don't like how Koopmans Senior designed his yachts? I've never heard of one falling apart.
If well built and well maintained, I see no reason why there should be any leakage or corrosion issues - even after 30 years. If she's as good as you say, the price seems about right to me but if she has been on the market for a while you may be able to talk the price down further.
If you like what you see, make sure
you get the boat professionally inspected before handing over any money. Preferably take the inspector with you if you can. No one should ever buy a steel boat, any steel boat, without first arranging an out-of-water survey.
Good luck!! I hope it works out for you.