You are correct: 3 on tibia (not counting sub-apical), 3 on first tarsal, 2 on second tarsal, and none on third tarsal.

so technically, 3,3,2 and all black keys to M. morula in Liljblad. But he was "uncertain" about the validity of the species. Overall, your beetle (and M. morula) is close to the M. aspersa group, which are 2,3,2 on the ridges - except at least M. aspersa itself mentions the sometimes presence of rudimentary ridge (making 3). Your beetle would not be aspersa itself as it's larger and more completely black, but if very well could be one of the others in the complex such as M. rubrilabris (also, yours seems likely to be a female - size + almost all black). In the end, I'd suggest we leave this at the genus level, at least until we get a non-taxon aspersa group page set up.

Thanks for the leg images - they are invaluable, even if we couldn't get to species on this one.

Oh, and the Goldenrod gall association is another thing in favor for aspersa group.