That thing uses an optical distributer with no servicable parts, and yes they where very prone to failure especially after they get hot. You can get rebuilts except like I said theres no servicable internals, meaning that they probally just clean em up We usta get a new one from the dealer but I'd bet they are no longer available plus they where a little pricey.
Since I'd bet your stuck getting a rebuilt one make sure it has a decent warranty as you might need it. Not uncommon to go thru several before you get one that will stay alive. I have coverted a couple of em back then with a kit, can't remember where I got it but it contained a pickup and a trigger wheel, may have been made by Pertronix.......