I'm sure someone will have choice words for what I'm about to say, but it does work and havent had to replace a OWB or starter shaft ever. If cleaning the OWB still results in slippage, I've used 400 or 600 grit wet/dry sandpaper (I call it abrasive) with a little ARO or light oil and just "rough up" the shaft just a teeny bit and have had good results. The key in doing this is to remove the backplate and starter shaft and sand/clean the shaft outside of the engine so there is no chance of the metal particles to get into the bushing on the rear of the engine. Just my 7½ cents.

Before reassembling I thoroughly clean with denatured alcohol.