shift lever fulcrum problems

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I'm looking for tips on how to get the fulcrum shift lever on my '50 C6 single lever transmission tighter without stripping the set screw. The spines on the fulcrum itself are gone but the splines on the shaft are good. The original 1/4" set screw was also stripped out so I've tapped new threads, 5/16 fine to get more bite. I've gotten tips of using JB weld, trying a small piece of paper over the spines etc. Also, there is only one compression spring at the top but none at the bottom but the 48-49 manual show two...top and bottom...but the '52 manual shows the same exploded view but only lists one. I'm not sure what the bottom spring would do. The two holes in the fulcrum in the first picture shouldn't be there, they were drilled and tapped by the previous owner for set screws.  Thanks,  Terry