Just wanted to chime in here to share a similar experience I've had and maybe to solicit some advice from those more knowledgeable about starters than I am.
'03 Jetta currently with ~366k mi - for the past 150k mi or so, I've replaced my battery about every 3 yrs, due to slow cranking when the temps got below 35F or so. The first couple of replacements were VW batteries from the dealer. The last couple were Wally World brand. This drove me nuts because I would have the "dying" battery checked at Wally World and was told they were well within range. So I would go to work every day through the winter, running outside during lunch break on really cold days to run the car for a while to ensure it would start for my ride home. I would eventually spring for a new battery and all would be well for another 2 or 3 years.
A year ago, I had 2 different Wally Worlds check it out, both times they said it was fine. I decided to pull the starter to clean and inspect it. I was not able to disassemble/detach the bendix? part mounted to the starter, but was able to clean out and re-lube the gears a bit.
Same problem after re-installing. Removed it again, tried and failed again to completely disassemble it, and decided to give it a whack with a hammer before re-installing this time. Guess what? Started like a champ every day for the next year! Oh, and because I still had one of my old VW batteries laying around, I charged it up and it starts my car as well as the new battery!
Now, just in the last week since temps are below 40F again, it's back to slow starting.
Not sure if I have the same problem, or a truly tired battery this time, as I haven't looked into it yet.
Anyway, what did I do when I whacked the starter? Is this a symptom of a starter needing replacement, or is there some other fix that doesn't include the need for a hammer? Any good how-tos for complete disassembly of this starter in case I attempt this again?
I don't know if this is Bill's issue, but the description sounded just like what I've been going through.