Cure my juddery brakes! Please!

I have 09 Magura Marta brakes on a steel hardtail. The forks are Rebas with a maxle and the front disk is a wavy 180mm rotor. Since being reunited with my bike after 18 months, the front brake has developed a serious judder when it’s applied.

Initially, I thought the pads may have been contaminated on its journey around the world. Or the rotor damaged. So I put new pads in and checked that rotor wasn’t warped. The judder disappeared for a couple of miles but is now back.

The headset is not loose. The bolts are all tight etc. Any other ideas what the problem might be? I did a google and there are reports 09 Magura Martas having this problem (perhaps due to the aforementioed wavy rotor) and Magura were offering replacement rotors. Anyone know if this was the case?

still sounds like contamination on the pads or rotor

I haven’t cleaned the rotor yet (its only the front brake) so will do that next.

I was surprised how much difference cleaning with disc brake cleaner made. The usual sanding, scrubbing with gravel etc didn’t help.
I just bought the Weldtite one as it was cheapest. Worked a treat.