Sadly these frames like many high end steel ones of this era get eaten away slowly by our damp oxidising atmosphere. Combined with riding water ingress into the ~ 0.4mm sealed seat tube its caveat emptor. Also seems to be fewer frame builders around to fill in holes or sleeve a section in neatly for sensible money + a repaint and shipping back and forth etc.
Cant see close up pics of this but the other small one on ebay looks pretty bad. Its a t shirt i have had in the past alas. Clean your Yos rust out and use frame saver liberally or buy a FAT Ti