It is entirely possible the PO installed a substandard rebuilt starter, leaving you in the same predicament he was in. Definitely an avenue to explore.
The PO of my 4.5 had 3 starters replaced in less than a year. In the 4.5's case it is shift column bushings (inside the steering column) causing slop. 4 going on 5 years, no starter replacements on my part.
'73 280SEL 4.5 (9/72)- RIP
Only 8,173 units built from 5/71 thru 11/72
'02 CLK320 Cabriolet - wifey's mid-life crisis
2012 VW Jetta Sportwagon TDI...at least its a diesel
Non illegitemae carborundum.