Starter works, solenoid new, why is it doing this?

I have a 1987 Volkswagen cabriolet that just decided not to start one day. I took it to someone and turned out the solenoid was bad, he put in a new solenoid and checked it with battery terminals and it went off like a blender!! Guy said the starter is still good.

I came back home, hooked it up and it fired up (after a few tries because of fuel filter problems). the car ran fine and even drove a short distance before being parked. Once parked, and fuel filter changed, I tried to start it with a different battery than the one I used first and it would not start. I head a grinding noise but it wont start.

someone is saying that the bushings are worn out and that is what is causing the problem, I think it may be the battery not having enough charge because it started before with a different one.
I just don't get it, it was definitely the solenoid the first time and with the new solenoid the starter (hooked up to a battery, not the car) went off like a blender!! Why then is it doing this now?

What is going on? do the bushings really are doing it? or is it the battery? I don't have the initial battery anymore so I cannot check it with that one again.