Mikebike:
Sorry. no idea. Most likely there is a replacement available. TI designs are top quality and it is unlikely they would use a super specialized component that cant be replaced. The trick is figuring out what writing on the transistor is important. There are often 2 or 3 lines of letters and numbers written on old transistors. The part number is hidden somewhere in one of those lines, or part of one of those lines. AND even then the numbers can be misleading. It may be something like a "NT540CL5" (i made that up). The part may be an NT450 NPN transistor, the "CL5" may imply that it has a higher operating range than the "CL6" or something. but all that matters is that its an NT450. AND it may only really matter that its an NPN... meaning you may be able to replace it with any old NPN transistor. this stuff can make you crazy. good luck!