[Oldteen]

An LBS just tried to tell me that my OP rims (<4k miles) are almost worn out because the fine milling lines on the braking surface are worn away in spots. Rim surface is otherwise flat (not concave from brake pad wear) & with no cracks or scarring. I've seen other rims, like newer Open Sport, with a deep distinct wear-groove which is supposed to indicate replacement time, but my OP's never had that when new. Plenty of OP's around here are still being ridden long after those braking surface millings have been completely worn off. Are all these experienced cyclists living on borrowed time?

 

[uncle]

What !

My OPs have roughly 20k on them and I live in very hilly area where lots of braking occurs.
Unless you've been descending wet, gritty roads with brakes on constantly, I don't know why your LBS would tell you that. That's ridiculous. At 4k they're just getting broken in. Rims are fine long after the original milling marks are gone. Ride on.