13 years later, I purchased a PL 518 with the dreaded foot rot. I went to the hardware store and bought (4) 7/8" table leg tips and (4) 1" tips. Investment was under $8.00. I used the original screws but removed the little disks of rubber that were clinging on. I screwed the 7/8" tips, upside down, one per corner. I then took the 1" and shoved one up over each of the 7/8" tips in the correct orientation (hole at top, base at bottom) (this required a little lubricant; I used saliva as it was handy and inexpensive). At first, they went on but popped back off when I stopped applying pressure. I solved this by drilling a small hole in the bottom of each of the 1" tips to let air escape. Once I did this, the 1" slipped up over the 7/8 " and held firmly. It works! I have never seen the original feet on a 518 as they are all rotted out. I don't have springs in mine, but if I wanted to, I could do that. Down the road, probably if I veneer the plinth and base, I will replace with something prettier, but for under $10.00, this was an easy fix. All credit to EVBoy who came up with the general idea.
