[Roadsters] Smoking/failing starter or something else?

[Ritchie Labate]

I need help with my '68 2000. About a year ago, I replaced the original starter with the recommended Nissan forklift gear-reduction type as posted on our wiki section. Worked fine for about 6 trips. Installed new headers, leaving the shop, 10 minutes later, I hear a high pitch whirling sound, then smoke from under the hood, I shut it down. Was told by a mechanic its the starter. I replaced it with another forklift starter, drove it maybe a dozen more times. Last weekend, started up in the garage, idled for 10 minutes when I went inside, came back, heard the whirling sound, then smoking. Immediately shut it down, looked underneath, saw smoke coming from starter, not able to start it again. What the heck?? Mechanic said maybe solenoid, not disengaging flywheel, and burning up the solder inside. It did smell like an electrical fire. Could it be anything else? Ignition system? Why does it appear to work a few times than fails? I'm hesitant to go ahead and
 throw in this new starter at this point. Should I take it to an electrical specialist to diagnose first?

Thanks!

Ritch