Am assuming you mean the Car ID sensor, not the slot guide opto-isolator sensor on the start/finish line...
The SMD sensors are generally unknown - however a larger device can be installed with a small bit of work. Off the top of my head I can't remember what the alternative is. Will find out for you.
If you have an unused PB6 or Digital Lap Counter, you could raid it for spares, and put that on. The very fact that you've worked out the fault probably means you have the skills to complete this swap-over.
Ian