Scott, you told that there's something that destroys input pins of your 74LCX245. As Richard already mentioned, this "something" must be a real heavy "something", because inputs of 74LCX245 a rather robust.

We told you first to look with a scope what is going on in your application. This not only to find a suited input protection for your LXCX245, but also for an other reason. There's still this limit switch in the motor. This can also be damagaed or even destroyed by the "something" that hits the switch line! And when the limit switch is not functioning properly, then total disaster can happen!

In this context please answer two another important questions:

1. This limit switch, does it open or close, when the motor reaches its limit? It should open, because then a break of cable or damage of limit switch will automatically stop the motor and prevent disaster.

2. The limit switch has one terminal connected to ground. What ground is it? Is it connected to protection earth at the motor, or is the ground terminal of limit switch connected to ground via the cable, also feeding the +5V?

The reason why need to know, whether the signal ground of your board (the ground which is connected to ground pin of 74LCX245) is connected to the ground of your limit switch is, because if not, then the "something" will run directly into the board (containing 74LCX245), even if there's a protection circuit! And imagine what happens if the "something" is an accidantal short to mains and this is injected into the board containing 74LCX245! In this case also the use of opto coupler wouldn't help much, unless the two sides of optocoupler are totally isolated.
If the limit switch supply is not isolated from the boards ground, then it would make sense to additionally fabricate a total isolated +5V supply, use this for the limit switch circuitry and insert a glavanic isolation to your board. This could be done by a simple relay, as Russell already mentioned, or by the use of an opto coupler.

But again, if the ground terminal of limit switch is connected directly to ground at the motor and if the limit switch is a closing type, then no solution we will ever find, will ever really protect your application!

We could propose a simple protection circuit and tell you, Scott use it and you will be fine. But that would be unprofessional! So, we try to find out, what the failure is, what this "something" is, how the grounds are connected to each other and how the limit switch is connected and works, just to find a proper way to help you. So it's not that we want to annoy you with our questions and the demand to answer them, but that we simply want to prevent a disaster that could hurt or even kill you!

The basis on any solution is measurement!!!!!!! Try to find out, what this "something" is, before you even think about a protection circuit!!

Kai