I'd suggest two improvements:
1. Start the formula in vCondition with the equal sign, in order to pick the relevant formula before the expression gets to the Chart Measure - that means that Measures cannot be your chart Dimension, but it will largely improve performance.
2. The parameter to the $-sign expansion needs to be enclosed in single quotes, to appear as a string:
I believe that these two changes should fix the problem, however everything needs to be tested :-)
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