How have you established the cross-over is at fault and not the tweeter?

The cross-over for the M60 is a custom design. You can't buy one off-the-shelf. You could replace faulty components though. There are many sources for them like Arrow Electronics.

I suppose if you don't have the cash, there's no point in me telling you the M60v4 is vastly superior to the M60Ti. The M3v4 is superior to the M80v2.

House of the Rising Sone
Out in the mid or far field
Dedicated mid-woofers are over-rated