Mower crunch

I've got an '89 Sears 30" rear engine riding mower. Today I had the misfortune of getting hung up on a low remnant stump. In the process the blade managed to cut into the deck itself.
I was able to free the blade and using a sledge drive the cut metal of the deck clear. The mower starts and drives properly until the blade control is engaged. At that time a crunching sound is heard and the engine wants to quit.
I've got the full owners manual with parts listing and diagram. Wondering where I should look first to identify the source of the crunch? When I freed the blade nothing was sticking.
With this in mind have I reached the point where repairs are going to exceed lasting value? Curious which areas go beyond the skills of an average homeowner tinkerer.
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Check out the "woodruff key". These are supposed to shear off if the blade gets jammed to prevent the shaft from being bent.
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Noozer wrote:

Other than the flywheel key the only one found marked key is an internal transmission part next to the Output and Brake Shaft. Is this likely what you mean?
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