Looks like a nice brown marble, TP. Hope you didn't pay too too much, but it's likely a pretty good table if the playfield is flat.
http://www.southernfoosball.com/images/TP2000-1.jpgI'd guess the holes were not drilled out... usually the nut / bolt fasteners chosen have a similar tolerance to the roll pins on tornado hollow type rods... I bet the guy got a deal on knock off tornado figures... and the bolt was necessary to attach them.
Regardless, as bolt115 has suggested there could be a problem from tolerance "slop" or unusual wear. If your interested in upgrading, I'd recommend buying a sample of the current tornado figure and roll pins to see if you can mount them solidly.
I wouldn't be too concerned about buying a new set of figures, you will get the modern foot style and the resin will be more elastic/robust. Conversely, you could likely find used "old" tornado figures for really cheap on ebay... myself, I have a dozen or so in a box from my recent upgrade... I suppose I keep them in case I come across someone or a table in need.