Probably aftermarket. A generic kit that has lots of parts for lots of Walbro carbs that you don't really need. When you search start the search line with OEM. jmho OThttps://www.dlastore.com/gasket-diaphragm-repair-kit-for-walbro-wa-wt-carburetor-series-k20wat.html
Does this seem thrustworthy ?
The diagram I posted is from DIY spare parts located in England. I go there often because they have diagrams on just about everything and list part numbers which often are not available here in the US. Especially on older saws. I get the part number and then search here at home. They show the impulse hose PN 19 in the diagram as 1123 141 8600. Search stihl and that number. wala! good number. And readily available. OTI think that you are right. Looks like a proprietary molded hose.
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