Just a bit more info* on part #87 it used to be part #83 so if your KSC glock is as old as mine your manual will say 83 but it is the same part.
The rocket valve (part #24 for KSC) breaking will also cause failure to cycle/blowback properly. and they do like to snap in half.
*Not sure how useful this info is as there seems to be less and less old glocks and old glock owners out there now.
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