yeah. that looks exactly like the lines on my marvics! my problem arised from a painter wet rubbing my wheels for paint and inadvertantly rubbing through the zinc di-chromate. neither the painter or myself knew the problems associated with his actions, but, i found a place that re plated my wheels and armed with the knowledge to know what can and can't be done i have had no problems since. 5 years and counting. for your sake (and the sake of your wallet) don't let them go too far, get them re-plated, re painted and ride it. i saw a 916 at a national rally here in 2000 that had those marks EVERYWHERE on both front and rear wheels, i tried to tell him how dangerous it was but he wasn't interested. glad i wasn't riding it, that's all i can say.
cheers,
paul.

As an aside - I was always led to believe Dymag were the peeps to contact wrt wheels manufactured by anyone, if there was any doubts about deterioration etc as they could not only x-ray / dyepen test them as necessary but advise on refurbishment.

I never did get around to contacting them about costs - but - the best don't come cheap I guess!

Cheers - Frank