Lots of noise printed here with little real knowledge of Italian Bimare boats: The bolt tube just keeps the sail in the track. I have replaced the tube in several Bimare A-cat sails that needed attention after several years of hard use.
The plastic tube is polyethylene, and the Bimare A-cats with Riba mast need a 5/16 inch tube (1/16 inch wall) available from any US scientific supply house (Fisher). (I used the same size polypropylene tubing for the last repair because it is a bit harder). You get 100 feet for $40 and need just 30 feet.
1. Cut the sewn threads that hold the crushed tube in place and pull it out of the sleeve.
2. Push 2 feet of line up inside the lower 2 feet of new tubing, and maybe a piece at the top, sew it in as before-- by hand.
3. Insert tubing from the bottom of the sail, sew in place at the top, then stretch to match, and sew at the bottom. Done. Do not even need to take the batten cap ends off
4. Do NOT buy metric sizes because the wall thickness is 1 mm which is too thin. It will crush.
5. 1/4 inch is too small and weak, and 3/8 inch tubing is probably too fat for your Riba mast, so check the stock tube.