I went through this winter with the old starter without getting stranded.
There were a few days where I had to plug in the block heater to get it started. The synthetic oil also helped I'm sure. This starter would crank at its already slow RPM for not more than 30 sec than slow down even more to where it would bog down. I finally pulled it and free spun it with a battery and it would spin fine for a few seconds and then slow down as if something was binding. I took it apart to find the bushing on the brush end of the armature was ovaled with a lot of play in it. That and the armature being dark from heat explains it. The stalling of the motor is very bad while power is being applied to the windings without work being done so all the juice goes into heating up the windings instead of doing work. Oh, the top bolt was missing so it made taking the starter out a bit easier. Also, the grease cap that protects the (worn) bushing was completely dry. The missing upper bolt likely contributed to the premature wear of the bushing.
I have a used starter which I disassembled, cleaned/ lubed, ready to go in. I hope this will end my starter problems.