I think I solved the mystery...This would explain why my shifter got so rattly in the last week or two:
https://www.wevo.com/Products/ShifterProducts/ShifterImages/WEVO_915_Shifter_INSTRUCTIONS_2009.pdf
25 - LC 026B 09 M - WEVO PLUNGER COIL SPRING
26 - 48200 - M10 X 10 SOCKET SET SCREW
27 - XT_144 - WEVO PLUNGER BUTTON