why mechanic replace valve cover for toyota camry 2000 v6

Why don't you ask them? Maybe it was cracked or warped.

If the valve cover was the source of the oil leak that's why they replaced it. I'm sure an original equipment Toyota valve cover is no longer available for your 20 year old vehicle! Hope that helps! Jim

PCV may be integral to the valve cover, so while they had it apart they replaced it.

The V6 Camry of that era had a problem with sludge building up between the top of the cover and the oil baffle which is an integral part of the cover. This buildup, when severe, can restrict the breather system. This allows internal pressure build up inside the motor, causing even more oil leaks. Problem is common when the oil is not changed regularly, but we have seen it on well maintained vehicles also. These covers do not readily lend themselves to cleaning; as such, it is usually more cost effective to just replace the cover. OEM covers tend to be horribly expensive, aftermarket covers are less expensive and generally work just fine. The only problem I see here is the dealer not contacting you before replacing the covers. Then again, they may have not been able to contact you, forcing them to make a judgement call as to whether to replace the covers. A really sharp service writer could have given you a heads up of this being a potential problem when the car was dropped off, and covered additional costs with you before the repair was started. Assuming to covers were clogged, replacement with aftermarket covers was the best call. Regular oil changes using synthetic oil usually prevents recurrence of the problem. Last thing, they did check/replace the PCV valve as well, right??