[Calum]

Originally Posted by makinen

I've installed Com-C mounts with RCE Tarmac springs and Koni Yellows.

This is a stock spring perch on the Koni Yellow.
Attachment 79871

And a spring perch without flat washer on the Koni.
Attachment 79872

With a conical washer. As you can see, the conical washer is slightly thicker than the flat welded washer.
Attachment 79873

Alignment spec:
Front camber -3, toe 0
Rear camber -2, toe 0

In the last year, it failed after a day of HPDE. Only the mounts are installed to the stock struts.
This time, they have survived after a day of HPDE on wet road plus over 600 km trip to and from the Korean International Circuit. Wet condition may give less load to the mounts but I think this signal is positive.

So drilling was the best way to get the flat washers off. Did you try any other method?