Get a new one!
A small harken car will cost about $80, the replacement track another $45. Before you spend that kind of money, call parts dept at catalina factory in Thousand Oaks,Calif. to see what they can do. Also try CatalinaDirect.com. Parts like that vary from year to year as Catalina changes suppliers. Replacing the traveller car is a very common upgrade and it definitely improves performance. I tried to fix an old Barton car on another boat I owned. Went to all the marine stores, even Minney's surplus in Newport Beach, Ca..... There was lots of stuff there, and it was fun to poke around, but I ended up buying a new one.