Intermittent starter problem - 03 Taurus

I’ve got a 2003 Ford Taurus, more than 200K miles on it. About nine months ago, it developed an intermittent starting problem. Every once in a while (probably less than 10 percent of the time), it had trouble starting. It wasn’t a battery problem. It would grunt a bit, and then stop. I took it to two different repair shops, left it for a couple days at each place. Both repair shops said they couldn’t replicate the problem. A week or two later, the starter died completely. I had it replaced and it worked fine.
Until last month. For the last 10-14 days I’ve had the same problem – every once in a while it doesn’t want to start. I took it back to the repair shop that replaced the starter last time, hoping the warranty might still be in effect. They just called to check in and say they can’t replicate the problem.
I drive a lot for work, so I really don’t wan to get stranded anywhere, but I’m not sure what to do. Should I just go ahead and wait til it gets worse? Replace the starter anyway? It’s pretty frustrating, and I’m not sure what to do. But I’d prefer not to just wait til I get stranded somewhere.

Did they check the battery this time? How about all the connections, including grounds? Has it had those aftermarket new battery cable ends installed? Those tend to corrode under the clamp where the cable attaches. If all of those are good, I’d say the new starter has gone south.