Mine had become increasingly reluctant to crank especially when cold so I planned to (and will still) remove the old starter and give it a clean and some tlc. However I also looked at my solenoid. I suspect it is not original being of open construction with the ability to dismantle and clean. So I did
The main contacts looked very dirty and pitted a bit so I rubbed then back to a shine with an emery board. Reassembled and 're installed the starter now cranks like the clappers before being given tlc and new brushes etc.So if your car is cranking slowly don't immediately blame the starter....maybe your solenoid on the near side next to the battery is the culprit....and it is far easier to remove