starter headaches

[JacobJob]

Hello everyone, this my first post. Been pouring over sites and stumbled upon this forum, and found many answers to my questions, thanks to all the knowledgeable posters

I bought a 1975 280 about 6 months ago and its just recently had a deluge of starter problems. The starter was replaced with a bosch rebuilt by the previous owner about a year ago. About a month or so ago the starter was staying engaged with the flywheel and continuing to run with ignition off creating that loud whining jet sound, so I immediately took it to get the starter replaced with another bosch rebuilt i ordered, I assumed it fried the starter and wasn't just the solenoid. This worked fine for awhile, then when cold weather set in, one morning I started it and it made a grinding noise and was not turning the engine on the second try it started up as usual. I replaced the battery. It did this intermittenly 4 or 5 times more, and now does it consistently. I'm planning on replacing it with yet another starter.
Is this just bad luck on starters? Is there something else that could be causing it eat starters? I never crank the starter for more than 10 seconds (1 second if it's grinding) so I dont think I damaged it that way.

I would greatly appreciate any info or help you can give me in this matter. thanks