Found a "back in the hills" chain saw guy that got all the dead saws from a big retailer. He had all the parts from a donor saw.
The 028WB (Not the later 028 AV) came without a chainbrake or it was an option then later got one of the first? chainbrakes. It's a kind of simple thing but worked well during my ownship, had it trip a time or two during use. While it wouldn't have been an injury it was nice to KNOW it was on duty.
* The chainbrake from an 028AV will not fit an 028WB *
The manual with part numbers conveniently found here;
https://www.arboristsite.com/threads/stihl-illustrated-parts-lists-ipl.317358/
028_IPL.pdf is the file you want, the chain brake is down a ways.
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Install was not difficult. Note you need the hand guard #26 also, it's different from the non brake part.