It's not a 11 series, it's a Series 5,1984 vintage. New Rotary shifters are $18.00 free shipping. If I going to the effort to replace a lever,I'd prefer to go with new.I can't find my folder for the 11 series mowers. I think your mower has the later style knob that pushes on rather than having the threaded knob? Snapper had at least four different styles of this lever. I have three used ones of this style. $13 ea for just the lever plus the shipping. Thought I had at least one new lever. Must have sold it.
I had a cemetery that ran three 30" standard deck RER. They traded for a new mower every other year. They would go through two shift levers every summer. I kept 2 levers and knobs in stock just for them.