Mavic ceramic rim - weld seam / oscilation under braking

I have an old ceramic rim on my functional bike. The rim surface is a bit glazed, but in decent enough condition, a bit pitted, but that tends to happen on these, nothing too severe. However I can feel the rotation of the rim under braking, as if the seam has been ground back and I can feel that passing the pads. It wouldn't bother me, but my fork is quite flexy and under heavy front braking it feels like I'm going to lose my fork, and hence my teeth. I can actually see it deflecting up to about 8mm :/

This only became noticable when I switched to V brakes - it's the extra braking force making it apparent I think.

I've checked the rim and it appears straight, I can see where the seam is, but it's not apparent on the braking surface. Do I have any options other than a new rim? Grinding disc to the braking surface?

V brakes can be more grabby compared to older type cantis.
Did you try toeing in the brake blocks a bit and cleaning the block surfaces.

That's a good idea. I'll give it a go, they need some attention anyway, haven't been touched in ages

I had a similar problem with an old Wolber Profil 18... the rim joint was such a bulge that every revolution it was almost ripping the brake caliper off the fork... eventually I got rid of it as I figured out there was nothing sensible I could do about it... That unless you have a machining workshop. Sandpaper won't do much, might just make it worse