Sounds like you are waking her up nicely. Weak closure you speak of: The engagement of gear is 100% your foot and the mechanism operation, the spin is the electrical circuit. As said, taking it out is cake. Inspection before taking out ,as best you can, may expose the problem. Once on bench you can operate it, clamp it down, hook a battery pos to post, neg to case. They come apart and are very easy to work on (don't read cheap). It does seem like your starter motor is good but the bendix is bad. I'm cheap also but have learned when to fix and when to buy. You will have to decide if it's fix or buy because we can't see it from here. But do play with it or inspect, you may see something obvious. Sometimes on the bench it will seem OK because it's not under load or in operating position. In that case you can't learn what's wrong unless you are experienced and have testing equipment. Otherwise it's a core!
